Articulo3

Contents lists available at ScienceDirect
Ore Geology Reviews
journal homepage: www.elsevier.com/locate/oregeorev
Short wavelength infrared (SWIR) spectroscopy of phyllosilicate minerals
from the Tonglushan Cu-Au-Fe deposit, Eastern China: New exploration
indicators for concealed skarn orebodies
Shitao Zhanga,b,⁎
, Gaobin Chua,b
, Jiamin Chenga,b
, Yu Zhangc,d
, Jing Tiana,b
, Jianping Lia,b
,
Siquan Sune
, Ketao Weif
a
CAS Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
b
University of Chinese Academy of Sciences, Beijing 100049, China
c
Key Laboratory of Metallogenic Prediction of Nonferrous Metals and Geological Environment Monitor (Central South University), Ministry of Education, Changsha
410083, China
d
School of Geosciences and Info-Physics, Central South University, Changsha 410083, China
e
Geological Survey of Hubei Province, Wuhan 430034, China
f
Team No. 1 of the Hubei Geological Bureau, Daye 435100, China
A R T I C L E I N F O
Keywords:
Short wavelength infrared (SWIR)
Chlorite
White mica
Kandite
Tonglushan Cu–Au–Fe skarn deposit
Eastern China
A B S T R A C T
The Middle–Lower Yangtze River Metallogenic Belt (MLYRB) is one of the most important Cu–Au–Fe–Mo skarn–-
porphyry metallogenic belts in Eastern China. After several decades of mining, the shallow-level mineral resources
have been gradually exhausted, which call for new exploration tools for concealed orebodies. The Tonglushan
Cu–Au–Fe skarn deposit (86.3 Mt @ 1.66% Cu, 0.94 g/t Au and 39.4% Fe) is located in the western MLYRB. Skarn
alteration/mineralization are mainly hosted in the contact zone between Cretaceous (~141 Ma) quartz mon-
zodiorite (and its porphyry) and the Lower Triassic carbonate rocks. Based on the mineral assemblages and their
macro/microscopic textural relationships, the Tonglushan Cu–Au–Fe mineralization/alteration can be divided into
five stages: pre-ore (S1: skarn–potassic alteration), Fe ore (S2: retrograde alteration and Fe-oxides), Cu–Au ore (S3:
quartz–sulfides), carbonate alteration (S4) and supergene alteration (S5). Apart from the major skarn and retrograde
alteration and carbonate minerals, abundant fine-grained phyllosilicate minerals, including chlorite, white mica
(illite, muscovite and phengite), smectite (montmorillonite and saponite) and kandite (kaolinite, dickite and hal-
loysite) group minerals have been identified at Tonglushan by SWIR spectrometry. Integrating petrographic ob-
servations and SWIR spectral analysis, four alteration zones (with distinct phyllosilicate assemblages) have been
distinguished from the intrusion outward: (I) ore-barren quartz monzodiorite and its porphyry (montmor-
illonite–illite–chlorite), (II) endoskarn close to the skarn–hydrothermal mineralization center (montmor-
illonite–illite–chlorite–kaolinite–dickite), (III) skarn–hydrothermal mineralization center (saponite–chlorite), and
(IV) the external contact zone in (dolomitic) marble (montmorillonite–chlorite ± kaolinite ± dickite).
For the Tonglushan altered rock samples, SWIR spectrometry has identified wavelength shifts in the Fe–OH,
Al–OH and sub-Al–OH absorption features of chlorite, white mica–montmorillonite and kandite, respectively.
Chlorite Fe–OH absorption occurs at longer wavelengths (> 2,250 nm), white mica–montmorillonite Al–OH
absorption occurs at unusually long (> 2,212 nm) and short (< 2,202 nm) wavelengths, and kandite sub-Al–OH
absorption occurs at longer wavelengths (> 2,170 nm) in strongly-altered skarn proximal samples. Moreover,
the presence of kaolinite, dickite, saponite, actinolite, phlogopite and/or chlorite–quartz–sulfides veins in these
samples can be used as new vectors to explore deep-level mineralization centers at Tonglushan. The distribution
of various kinds of phyllosilicate alteration minerals at Tonglushan, especially the white mica and kandites (with
higher crystallinity) in the deep contact zones, indicates that the neutral to acidic hydrothermal fluids may have
been generated with the precipitation of Fe-oxides and sulfides. This study also highlights the potential of SWIR
spectroscopy of phyllosilicate minerals for exploring concealed skarn orebodies in the MLYRB.
https://doi.org/10.1016/j.oregeorev.2020.103516
Received 29 December 2019; Received in revised form 21 March 2020; Accepted 1 April 2020
⁎
Corresponding author at: CAS Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou
510640, China.
E-mail address: shitaozhang@gig.ac.cn (S. Zhang).
Ore Geology Reviews 122 (2020) 103516
Available online 03 April 2020
0169-1368/ © 2020 Elsevier B.V. All rights reserved.
T

1. Introduction
Prediction and exploration for concealed magmatic–hydrothermal
orebodies remain a major challenge in the global mineral industry, due
to the limited geological information yielded from conventional
shallow-level geological surveying tools (McIntosh, 2010; Cooke et al.,
2014). In recent years, short wavelength infrared (SWIR) spectroscopy
have been successfully applied in mineral exploration and ore deposit
studies, especially in porphyry–epithermal-type and volcanogenic
massive sulfide (VMS) systems (e.g., Herrmann et al., 2001; Sun et al.,
2001; Jones et al., 2005; Yang et al., 2005; Chang et al., 2011; Laakso
et al., 2016; Huang et al., 2018; Feng et al., 2019). SWIR can be very
effective in identifying common phyllosilicates, carbonates, sulfates,
OH-bearing and NH4-bearing minerals. Meanwhile, the technique can
directly vector toward the hydrothermal center using the reflectance
spectral features of the typical minerals (Thompson et al., 2009; Chang
and Yang, 2012). For instance, studies on the Lepanto high-sulfidation
(HS) epithermal Cu–Au deposit (Philippines) found that the longer
wavelength of alunite 1480 nm absorption position (Pos1480) is closely
related to the distance from the hydrothermal center (Chang et al.,
2011), whilst the shorter wavelength of Al–OH absorption position
(Pos2200) of white mica is correlated with the hydrothermal center of
the Pebble porphyry Cu–Au–Mo deposit in Alaska (Harraden et al.,
2013). However, application of SWIR spectroscopy in skarn-type de-
posit exploration was scarcely reported.
The Middle–Lower Yangtze River Metallogenic Belt (MLYRB) is the
most important Cu, Fe and Au skarn mineral province in China, and
attracted much attention in the past several decades (e.g., Chang et al.,
1991; Zhai et al., 1992; Zhou et al., 2015; Li et al., 2009, 2014; Xie
et al., 2011b; Chang et al., 2019). The Tonglushan deposit is the largest
Cu–Au–Fe polymetallic skarn deposit in the MLYRB, and has been
studied for its geology, age, petrogeochemistry, skarn mineral para-
genesis and compositions, together with certain aspects of ore-forming
fluids (e.g., Shu et al., 1992; Wei et al., 2007; Xie et al., 2011b; Li et al.,
2010; Zhao et al., 2010, 2012a, b; Duan and Jiang, 2017; Zhang et al.,
2018). After several decades of continuous mining, the Tonglushan and
other similar skarn–porphyry deposits in the MLYRB are gradually ex-
hausted, and continued mining operation would require the discovery
of more concealed orebodies. In the past decade, some concealed or-
ebodies have been discovered in the Tonglushan ore field, such as the
Tonglushan No. 13 orebody and the Jiguanzui No. 7 orebody (Hu et al.,
2011; Zhang et al., 2018; Tian et al., 2019). These new discoveries can
serve as case study for the application of alteration and SWIR spectral
characteristics, and provide indicative information for the skarn
(–porphyry)-type deposits in the MLYRB.
In this contribution, we present detailed characteristics of alteration
minerals from the newly discovered Tonglushan No. 13, 3 and 4 or-
ebodies. We describe their geologic occurrences, alteration/miner-
alization paragenesis, distribution patterns and zonation. We
then refine the use of SWIR spectral features of chlorite, white mica–-
montmorillonite and kandite as effective tools for mineral prospecting.
Moreover, we carry out a comprehensive comparison with porphyry
and VMS deposits to explore the potential of alteration minerals in
exploring different types of magmatic–hydrothermal deposits.
2. Geological setting
2.1. Middle–Lower Yangtze River Metallogenic Belt (MLYRB)
The Middle–Lower Yangtze River Metallogenic Belt (MLYRB) lies in
the tectonic junction of the Yangtze Craton, North China Craton and
Qinling–Dabie Orogen, and is one of the most important Cu–Au–Fe
skarn provinces in Eastern China. The MLYRB consists of the Edong,
Jiurui, Anqing–Guichi, Tongling, Luzong, Ningwu and Ningzhen ore
districts from west to east (Fig. 1a; Chang et al., 1991; Mao et al., 2011).
The ore belt is bounded by the Xiangfan–Guangji Fault (XGF) to the
northwest, Tangcheng–Lujiang Fault (TLF) to the northeast and the
Yangxin–Changzhou Fault (YCF) to the south (Fig. 1a; Chang et al.,
1991; Zhai et al., 1996). Cambrian-Lower Triassic submarine clastic/
carbonate rocks and Middle Triassic-Cretaceous terrigenous volcanic-
clastic interbeds are widely exposed in the region (Chang et al., 1991;
Zhai et al., 1992; Mao et al., 2011).
In the past decades, many Cu–Au–Fe–Mo skarn and porphyry de-
posits and iron oxide–apatite (IOA) deposits have been discovered in
the MLYRB. These deposits are spatially associated with the Early
Cretaceous (ca. 152–123 Ma) mafic to intermediate–felsic magmatic
rocks (Fig. 1a; Mao et al., 2011; Zhou et al., 2015). Ore deposits and
related igneous rocks can be divided into four groups: (1) Cu–Au–-
Fe–Mo skarn–porphyry deposits associated with coeval high-K calc-al-
kaline intrusions (I type/magnetite type), e.g., diorite, quartz diorite
and granodiorite (ca. 152–135 Ma); (2) iron oxide–apatite (IOA) de-
posits associated with coeval Na-rich calc-alkaline dioritic intrusions
and their volcanic equivalence (ca. 135–125 Ma); (3) Fe skarn deposits
related to the Early Cretaceous granites (ca. 133–127 Ma); and (4)
minor Cu–Au hydrothermal veins associated with A-type granitoids and
alkaline volcanic rocks (ca. 127–123 Ma) (Fig. 1a; Chang et al., 1991;
Mao et al., 2011; Zhou et al., 2017).
2.2. Edong ore district
The district is located in the western MLYRB, and is one of the most
important Cu–Au and Fe skarn ore districts in Eastern China (Xie et al.,
2011b; Li et al., 2014). Local exposed stratigraphy ranges from Paleo-
zoic to Cenozoic. Late Paleozoic metamorphic rocks are only exposed
locally in the southern Edong. The Cambrian to Middle Triassic marine
carbonate and turbiditic clastic rocks are widespread, with a total
thickness of over 6 km, and Upper Triassic to Middle Jurassic clastic
rocks also outcrop locally (Fig. 1b; Shu et al., 1992; Li et al., 2009).
Early Cretaceous volcanic rocks in the Jinniu basin are mainly exposed
in the southwestern Edong. Zircon U–Pb dating indicates that the vol-
canic rocks were mainly formed in ca. 130–125 Ma (Fig. 1b; Xie et al.,
2011a; Li et al., 2012). In this district, the (dolomitic)-marble and
sandstone-shale of the Triassic Daye Formation (Fm.) are the most
important ore host (Chang et al., 1991; Shu et al., 1992; Xie et al.,
2011b).
Late Mesozoic intermediate-felsic intrusions are widespread in the
district, covering a total area of ~700 km2
(Fig. 1b). It consists of six
large plutons, namely Echeng (granite and granite porphyry), Tieshan
(quartz diorite and diorite), Jinshandian (quartz monzonite, monzo-
granite and diorite), Lingxiang (diorite and quartz diorite), Yinzu
(quartz diorite) and Yangxin (quartz diorite), which occur with many
other stocks of granodiorite porphyry, granite porphyry and porphyritic
diorite (Fig. 1b; Shu et al., 1992; Li et al., 2009, 2014). In addition,
there are many dykes, including monzonite, syenite, diorite, gabbro,
diabase and lamprophyre ones, which intruded these large plutons (Shu
et al., 1992; Li et al., 2010; Bai et al., 2015; Zhang et al., 2018). Skarn
(–porphyry) deposits are commonly developed around these plutons
(Fig. 1b). For example, Cu–Fe (–Au) skarn deposits occur around the
Yangxin and Tieshan plutons, and Fe skarn deposits around the Echeng
and Jinshandian plutons (Fig. 1b). Moreover, some Cu–Mo and
W–Cu–Mo skarn–porphyry deposits (e.g., Tongshankou, Longjiaoshan
and Ruanjiawan) discovered in recent years are related to granodiorite
porphyry and quartz diorite stocks (Fig. 1b; Deng et al., 2015; Lei et al.,
2018).
3. Geology of the Tonglushan Cu–Au–Fe deposit
The Tonglushan Cu–Au–Fe deposit (30°04′30″ N, 114°55′42″ E) is
located about 3 km southwest of the Daye city (Hubei Province), with
proven ore reserves of 86.3 Mt @ 1.66% Cu, 0.94 g/t Au and 39.4% Fe
(Li et al., 2010; Zhang et al., 2018, 2019). It has a long mining history
dating back to the ancient Shang Dynasty (1600 ~ 1046 B.C.).
S. Zhang, et al. Ore Geology Reviews 122 (2020) 103516
2

Fig. 1. (a) Location of the Edong ore district in the Middle-Lower Yangtze River Metallogenic Belt (MLYRB) in Eastern China (modified after Mao et al., 2011). TLF:
Tancheng–Lujiang Fault; XGF: Xiangfan–Guangji Fault; YCF: Yangxing-Changzhou Fault; (b) Geologic map of the Edong ore district, showing the major types of ore
deposits (modified after Shu et al., 1992; Xie et al., 2011b, 2015).
3

Exposed stratigraphy at Tonglushan include the Lower Triassic Daye
Fm. limestone and dolomite, which can be divided into four members
(T1dy1
–T1dy4
) from bottom up (Fig. 2; Wei et al., 2007; Zhao et al.,
2012b). The Triassic NWW- to EW-trending folds and faults are devel-
oped, which are overprinted/crosscut by Jurassic and Cretaceous NNE-
trending folds and faults. The carbonates were metamorphosed to
(dolomitic)-marble and/or altered to skarn, which occur as concealed
and discontinuous NNE-trending blocks (Fig. 2; Liu et al., 2005; Wei
et al., 2007; Zhang et al., 2018, 2019). Major ore-related intrusive rocks
at Tonglushan are the quartz monzodiorite and its porphyry (Fig. 2; Li
et al., 2010; Zhang et al., 2018).
The quartz monzodiorite, which are spatially and genetically
related to the Cu–Au–Fe skarn mineralization, is widely distributed
at Tonglushan. It intruded the Triassic carbonate rocks at
141.0 ± 0.8 Ma, and consists of plagioclase (ca. 50–60 vol%), horn-
blende (ca. 15 vol%), K-feldspar (ca. 15–20vol%), quartz (ca. 10–15 vol
%) and minor biotite, with accessory magnetite, titanite, apatite, zircon
and monazite (Zhang et al., 2018). The quartz monzodiorite samples
are SiO2-rich (62.51–66.95 wt%), relatively high in total alkalis
(K2O + Na2O = 5.67–9.63 wt%) with A/CNK [Al2O3/
(CaO + Na2O + K2O)] of 0.73 to 0.90 (Zhao et al., 2010; Zhang et al.,
2018). They are rich in light rare earth elements (LREE) and large ion
lithophile elements (LILE), but relatively depleted in Nb, Ta and Ti
contents, and show I-type and magnetite-series affinity (Zhao et al.,
2010; Zhang et al., 2018). Moreover, Sr–Nd–Pb–Hf isotope geochem-
istry indicates that the quartz monzodiorite was mainly derived from
enriched lithospheric mantle and had experienced lower crustal con-
tamination and fractional crystallization (Li et al., 2009; Zhao et al.,
2010; Xie et al., 2011b).
Quartz monzodiorite porphyry has been recently discovered at
depth in the Tonglushan deposit. The porphyry was zircon U–Pb dated
(141.3 ± 1.1 Ma) to be coeval with the ore-related quartz mon-
zodiorite, and has similar mineral contents, and elemental and isotope
geochemical features to its equigranular counterpart (Zhang et al.,
2018). This indicates that the two rocks are comagmatic (Zhang et al.,
2018). Late dykes, including lamprophyre, granite and diorite porphyry
ones, intruded the quartz monzodiorite, skarns and Cu–Au–Fe or-
ebodies at Tonglushan (Fig. 2; Li et al., 2010; Bai et al., 2015).
Fig. 2. Simplified geologic map of the Tonglushan Cu–Au–Fe skarn deposit (modified after Li et al., 2010; Zhang et al., 2018).
4

Thirteen Cu–Au–Fe skarn-type orebodies and local Cu–Au breccia-
type orebodies have been discovered at Tonglushan (Fig. 2; Liu et al.,
2005; Zhao et al., 2012; Zhang et al., 2018), among which the No. 1, 3,
4 and 13 orebodies are more important (Fig. 2). These lenticular/stra-
tiform orebodies are mainly distributed along NNE-trending faults and
the intrusive contact between the quartz monzodiorite (porphyry) and
the (dolomitic)-marble (Figs. 2 and 3). In recent years, the concealed
No. 13 orebody was discovered in the contact zone between (dolo-
mitic)-marble blocks and the quartz monzodiorite (porphyry) (Figs. 2
and 3; Hu et al., 2011; Zhang et al., 2018). This orebody is mainly
distributed at −365 to −1275 m depth, consists of one main orebody
and five smaller orebodies (ca. 110–800 m long, ca. 600 m wide), and
dips SE at 45° to 75° (Fig. 3; Hu et al., 2011; Zhang et al., 2018).
Ore textures are mainly euhedral to anhedral, metasomatic, rimmed
and net-like, and ore structures mainly include massive, vein, dis-
seminated and locally breccia (Zhang et al., 2018). Field and lab pet-
rographic observations show that the ore minerals comprise dominantly
chalcopyrite, bornite, magnetite and hematite, followed by chalcocite,
azurite, molybdenite, pyrite, specularite and native gold. Gangue mi-
nerals are dominated by garnet, diopside, phlogopite, serpentine, epi-
dote, actinolite, chlorite, quartz, calcite and K-feldspar (Fig. 4).
4. Alteration and paragenesis
Due to contact metamorphism and subsequent metasomatism, the
Tonglushan quartz monzodiorite (porphyry) and carbonate wallrocks
were intensely altered. The alteration formed a complex calc-/
magnesian-silicate mineral assemblage, dominated by prograde garnet
and pyroxene and coeval potassic minerals, followed by retrograde
epidote, actinolite, phlogopite, serpentine and tremolite, together with
a wide range of phyllosilicate minerals (Fig. 4).
4.1. Alteration of intrusive rocks
The quartz monzodiorite has undergone various degrees of potassic,
garnet, diopside, calcite, chlorite, illite, montmorillonite, kaolinite and
dickite alteration (Fig. 5a-m). From the internal contact zone inward to
the ore-barren quartz monzodiorite, the diversity and intensity of al-
teration gradually weakened. Near the intrusive contact, the potassic,
garnet and diopside alterations were overprinted by epidote alteration
(Fig. 5a), and intruded by actinolite–biotite–magnetite–quartz–titani-
te–apatite veins (Fig. 5b, c) or actinolite–titanite–pyrite–calcite veins
(Fig. 5d). It is also observed that the quartz monzodiorite with
K-feldspar–(biotite) veins was intruded by quartz–calcite–-
chlorite–chalcopyrite–pyrite–molybdenite veins (Fig. 5e), pyrite–-
chlorite–quartz–calcite veins (Fig. 5f, g) and molybdenite–pyrite veins
(Fig. 5h). Some late-stage calcite–pyrite veins were also found cutting
the molybdenite–pyrite veins.
In addition, intensive kaolinite, dickite, chlorite, illite and mon-
tmorillonite alterations were also identified in the quartz monzodiorite
near the intrusive contact (Fig. 5i-m). In the quartz monzodiorite hand-
specimens, the K-feldspar alteration was overprinted by intense chlorite
and kaolinite alterations (Fig. 5i). In backscattered electron (BSE)
imaging, plagioclase in the quartz monzodiorite was clearly replaced by
Fig. 3. Geologic map of prospecting-line of 4# and cross-section A–A’ at Tonglushan, showing the spatial distribution of SWIR-analyzed samples.
5

kaolinite (Fig. 5j). Chlorite is another common alteration mineral
in the quartz monzodiorite. Near the intrusive contact, the
quartz monzodiorite was intruded/partially replaced by chlor-
ite–quartz–chalcopyrite (–pyrite) veins (Fig. 5k), and the magmatic
hornblende and biotite were replaced by chlorite (Fig. 5l). Further away
from the intrusive contact, weak potassic, chlorite, illite and mon-
tmorillonite alterations are present in the ore-barren quartz mon-
zodiorite, where the corroded magmatic hornblende/biotite grain
margin was rimmed by chlorite (Fig. 5m).
In/around the deeper parts of the intrusive contact, the quartz
monzodiorite porphyry was also intensively altered (potassic, diopside,
garnet, illite, chlorite, kaolinite and dickite) (Fig. 5n–r). In hand spe-
cimens and under the microscope, it is observed that plagioclase and K-
feldspar were replaced by diopside (Fig. 5n, o). Moreover, the porphyry
was strongly potassic-/illite-/kaolinite-altered, and locally cut by acti-
nolite–titanite–quartz–calcite veins (Fig. 5p, q). Under the microscope,
the plagioclase phenocrysts are almost completely replaced by kaolinite
and then cut by calcite veins (Fig. 5r).
4.2. Alteration of wall rocks and mineral paragenesis
At Tonglushan, the skarn and retrograde alteration and Cu–Au–Fe
mineralization occurred mainly in the external intrusive contact
(Fig. 3). Based on the mineral assemblages and their macro/micro-
scopic textural relationships, five alteration/mineralization stages have
been distinguished, i.e., (S1) the pre-ore (skarn–potassic alteration),
(S2) Fe ore (retrograde alteration and Fe-oxide mineralization), (S3)
Cu–Au ore (quartz–sulfides mineralization), (S4) carbonate alteration,
and (S5) supergene alteration (Fig. 4).
4.2.1. Pre-ore skarn–potassic alteration (S1)
The alteration is mainly represented by abundant anhydrous mi-
nerals in the endo- and exoskarn zones (Fig. 4). Three generations of
garnet (Grt1 to Grt3) are recognized, among which Grt1 and Grt2 are
pre-ore (Fig. 4). Grt1 is commonly dark brown to dark green in hand
specimens and full-dull under cross-polarized light (Fig. 6a-b), while
light brown/green Grt2 usually grows along the side of Grt1 and has
Fig. 4. Paragenetic sequence of alteration minerals from the Tonglushan Cu–Au–Fe skarn deposit.
6

distinctive oscillatory zoning (Fig. 6a-b). Further away from the in-
trusive contact, Grt1 is observed coexisting with diopside/wollastonite
in the exoskarn (Fig. 6c). Meanwhile, potassic/garnet/diopside altera-
tions were also developed in the quartz monzodiorite (porphyry)
(Fig. 5).
4.2.2. Retrograde alteration and Fe-oxides mineralization (S2)
In marble, epidote–quartz–specularite and epidote–actinolite–apa-
tite replacing Grt1 can be observed (Fig. 6d, e). Whereas in dolomitic
marble, phlogopite–magnetite (–serpentine) replaced diopside (Fig. 6f).
The alteration is accompanied by extensive magnetite and hematite
mineralization (Fig. 4). Spatially, the hematite orebodies mainly occur
Fig. 5. Photographs and photomicrographs showing typical alteration mineral assemblages and veins in the quartz monzodiorite (porphyry) at Tonglushan: (a)
Potassic, garnet and diopside alterations in quartz monzodiorite were overprinted by epidote alteration; (b and c) Potassic-altered quartz monzodiorite intruded by
actinolite–biotite–magnetite–quartz–titanite–apatite veins; (d) Potassic-altered quartz monzodiorite intruded by actinolite–titanite veins and then by pyrite–calcite;
(e) Potassic-altered quartz monzodiorite cut by quartz–calcite–chlorite–chalcopyrite–pyrite–molybdenite veins; (f and g) Potassic-altered quartz monzodiorite cut by
pyrite–chlorite–quartz–calcite veins; (h) Quartz monzodiorite cut by K-feldspar–biotite veins and then by molybdenite–pyrite veins, and eventually by calcite–pyrite
veins; (i) Potassic-altered quartz monzodiorite was overprinted by intense chlorite-kaolinite alteration; (j) Plagioclase in quartz monzodiorite replaced by kaolinite;
(k) Chlorite–quartz–chalcopyrite vein in quartz monzodiorite; (l) Hornblende and biotite in quartz monzodiorite replaced by chlorite; (m) Margin of biotite in quartz
monzodiorite replaced by chlorite; (n and o) Quartz monzodiorite porphyry replaced by diopside; (p) Quartz monzodiorite porphyry affected by strong potassic, illite
and kaolinite alterations; (q) Potassic-/illite-altered quartz monzodiorite porphyry cut by actinolite–titanite–quartz–calcite veins; (r) Plagioclase phenocrysts almost
completely replaced by kaolinite and then cut by late calcite veins. Abbreviations: Di = diopside, Ep = epidote, Grt = garnet, Kfs = K-feldspar, Act = actinolite,
Bt = biotite, Mt = magnetite, Qtz = quartz, Ttn = titanite, Ap = apatite, Cal = calcite, Py = pyrite, Chl = chlorite, Ccp = chalcopyrite, Mo = molybdenite,
Kln = kaolinite, Pl = plagioclase, Hb = hornblende, Ill = illite.
7

in the middle and shallow parts of the (dolomitic)-marbles (Fig. 6g);
while the magnetite orebodies are closely related to the skarn and
retrograde alteration (Fig. 6h). Under the microscope, it is observed
that saponite–epidote replaced Grt1, and the phlogopite–serpentine–-
saponite assemblage is cut by late calcite veins (Fig. 6i, j). In this stage,
epidote, actinolite, magnetite and biotite alteration also occur in the
quartz monzodiorite (porphyry) (Fig. 5a-d, q).
4.2.3. Quartz-sulfides mineralization (S3)
At this main Cu–Au ore stage, ore minerals include mainly chalco-
pyrite, bornite, chalcocite and pyrite, with local molybdenite, spha-
lerite, digenite and native gold. Gangue minerals include mainly quartz,
Fig. 6. Photographs and photomicrographs showing typical alteration/mineralization features in the external intrusive contact (in (dolomitic)-marble) at
Tonglushan: (a) Two pre–ore generations of garnet (Grt1 and Grt2), with dark-brown/-green Grt1 surrounded by light-brown/-yellow Grt2; (b) Homogeneous Grt1
(total extinction under crossed–polar) surrounded by oscillatory-zoned Grt2; (c) Pre-ore garnet–diopside skarn replaced by disseminated pyrite and pyrite–calcite
veins; (d) Epidote–quartz–specularite replaced Grt1; (e) Epidote–actinolite–apatite replaced Grt1; (f) Phlogopite–magnetite replaced diopside; (g) Massive hematite
ore overprinted by disseminated chalcopyrite mineralization; (h) Massive magnetite ore, with metasomatic residual diopside being replaced by disseminated
chalcopyrite; (i) Saponite–epidote replaced Grt1; (j) Phlogopite–serpentine–saponite cut by calcite veins; (k) Magnetite–hematite–phlogopite replaced Grt1 and then
by chalcopyrite; (l) Chalcocite–bornite–digenite assemblage in marble; (m) Disseminated chalcopyrite–sphalerite replaced magnetite, and then cut/replaced by
calcite–ankerite veins.; (n) Massive magnetite ore with metasomatic residual diopside cut by Grt3–calcite veins; (o) Chlorite replaced epidote; (p) Chlorite replaced
magnetite; (q) Hematite–kaolinite ores; (r) Hematite ore replaced by kaolinite–bornite, and then overprinted by goethite supergene alteration. Abbreviations:
Grt = garnet, Cal = calcite, Di = diopside, Py = pyrite, Chl = chlorite, Qtz = quartz, Ep = epidote, Spe = specularite, Act = actinolite, Phl = phlogopite,
Mt = magnetite, Hm = hematite, Ccp = chalcopyrite, Snt = saponite, Cal = calcite, Srp = serpentine, Ank = ankerite, Kln = kaolinite, Bn = bornite,
Gt = goethite. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
8

calcite and Grt3 (Fig. 4; Zhao et al., 2012b). Under the microscope,
magnetite–hematite–phlogopite replaced Grt1, which is in turn re-
placed by chalcopyrite (Fig. 6k). The chalcocite–bornite–digenite as-
semblage is also observed in the marble (Fig. 6l). Disseminated chal-
copyrite–sphalerite is found to replace the magnetite ore, and the latter
is also cut by Grt3–calcite veins with residual diopside (Fig. 6m, n).
Chlorite is one of the most important alteration minerals at this
stage. Apart from the chlorite-bearing quartz–sulfides veins (with K-
feldspar alteration halos) cutting the quartz monzodiorite in the in-
ternal intrusive contact (Fig. 5e-g, k), it is also observed (under the
microscope) that chlorite replaced epidote and pyrite–chlorite veins cut
the magnetite–hematite ores (Fig. 6o, p). Overall, chlorite can be di-
vided into three types of occurrences, i.e., DC-type: disseminated
chlorite replacing hornblende/biotite in the quartz monzodiorite (por-
phyry) (S1 and S2) (Fig. 5l, m); (ii) VC-type: chlorite–quartz–sulfides
veins in the internal intrusive contact close to the skarn–hydrothermal
ore center (S2) (Fig. 5f, k); and (iii) RC-type: chlorite replacing
epidote, garnet or magnetite in the skarn–hydrothermal ore center (S3)
(Fig. 6o, p).
Kaolinite is locally developed in the hematite orebodies (Fig. 6q).
Fig. 7. Diagram of drill core sample distribution in the Tonglushan skarn deposit.
9

Fig. 8. Distribution features of the retrograde alteration and carbonate minerals (a, b) and phyllosilicate minerals (c, d) in prospecting-line 4# and cross-section A–A’
at Tonglushan.
10

Under the microscope, hematite is replaced by kaolinite–bornite and
then overprinted by supergene goethite (Fig. 6r). Moreover, phyllosi-
licates of higher crystallinity (i.e., dickite, muscovite, and illite and
montmorillonite) in the deeper parts of Tonglushan are identified in
this ore stage (Fig. 4).
4.2.4. Carbonate (S4) and supergene (S5) alteration
Carbonate alteration was characterized by the formation of large
amounts of calcite ± ankerite ± pyrite veins crosscutting the skarn,
Fe-oxides and quartz–sulfides ores, and locally the quartz monzodiorite
(porphyry) (Fig. 5h, n and 6 m). Phyllosilicates of lower crystallinity
(i.e., kaolinite, illite and montmorillonite) are also identified (Fig. 4).
Abundant S5 supergene malachite and azurite occur in the shallow
parts of the No. 1, 3 and 8 orebodies (Fig. 4; Zhao and Lin, 1990; Shu
et al., 1992). Some lowest-crystallinity phyllosilicate minerals, such as
halloysite, montmorillonite and kaolinite, are also identified (Fig. 4).
5. Sampling and analytical methods
A total of 2,636 rock samples were collected from 20 drill holes at
Tonglushan (Fig. 7; Tables S1–S4). Part of the drilling sections have no
samples collected since the drill core were lost during the mining his-
tory (Figs. 3 and 7). The sampling interval was generally about ~6 m,
and decreases with increasing rock-type variation and alteration/mi-
neralization intensity (Figs. 3 and 7). All collected samples were SWIR
spectral analyzed, and polished thin sections for 620 representative
samples were prepared and observed under the microscope.
All drill-core samples prepared for SWIR spectral analysis were
cleaned and dried to avoid any interference from surficial impurities.
About 7,908 near–infrared and short wavelength infrared (SWIR)
spectral data were obtained with a Terra Spec 4 Hi–Res Mineral
Spectrometer (Analytical Spectral Device (ASD), Inc (USA)). Three
analysis spots were commonly measured on each sample. The RS3
software was used to collect the SWIR spectra. Detailed equipment
settings and procedures are as given by Chang and Yang (2012).
All obtained data were automatically interpreted by The Spectral
Geologist (TSG) software based on the wavelength, shape and intensity
of the main absorption features in each spectrum. Then, the spectra
were manually compared with the TSG reference library to accurately
identify the minerals and abundance ratios. The major quantitative
parameters, including wavelength position (Pos) and absorption depth
(Dep) of H2O, Al–OH, sub-Al–OH, Fe–OH and Mg–OH absorption fea-
tures and illite (white mica) crystallinity (IC = Dep2200/Dep1900),
were extracted by using the TSG scalar function. Detailed settings for
the acquisition parameters were as outlined in Chang et al. (2011) and
Chang and Yang (2012).
6. SWIR spectral features of phyllosilicate minerals
6.1. Types and zonation of phyllosilicate minerals
Based on the SWIR spectral analysis, about 20 types of alteration
minerals have been identified, including retrograde alteration minerals
(epidote, actinolite, tremolite, phlogopite, serpentine and talc), carbo-
nates (calcite, ankerite and dolomite), chlorite, white mica (illite,
muscovite and phengite), smectite (montmorillonite and saponite) and
kandite group minerals (kaolinite, dickite and halloysite) and minor
prehnite. The spatial distribution of these minerals are illustrated in
Fig. 9. Standard spectral curves of phyllosilicate minerals. (a) Chlorite group (Mg-chlorite, Int-chlorite and Fe-chlorite); (b) White mica group (illite, muscovite and
phengite) and montmorillonite; (c) Kandite group (kaolinite, dickite and halloysite); (d) Smectite group (saponite, nontronite and montmorillonite).
11

Fig. 8. The retrograde alteration minerals have a close spatial link with
(garnet)-diopside skarns, with some of actinolite and phlogopite oc-
curring in the quartz monzodiorite (porphyry) (Fig. 8a–b). The SWIR-
identified carbonate minerals, including the hydrothermal calcite and
ankerite, and the original calcite and dolomite in the (dolomitic)-
marble are discontinuously distributed (Fig. 8a–b).
Phyllosilicate minerals, including chlorite, white mica, smectite and
kandite group minerals are widespread at Tonglushan (Fig. 8c, d).
Based on the mineral assemblages and spatial distribution character-
istics, from the internal to external intrusive contact, four alteration
zones (zone I to IV, each with distinct phyllosilicate assemblages) have
been distinguished: (I) ore-barren quartz monzodiorite (porphyry)
(montmorillonite–illite–chlorite alteration), (II) internal intrusive con-
tact close to the hydrothermal center (montmorillonite–illite–-
chlorite–kaolinite–dickite), (III) skarn–hydrothermal center (saponi-
te–chlorite), and (IV) external intrusive contact in the (dolomitic)-
marble (montmorillonite–chlorite ± kaolinite ± dickite) (Fig. 8c, d).
Within each phyllosilicate group, e.g., white mica (illite, muscovite and
phengite), the minerals have similar SWIR spectral features (Fig. 9). In
this study, we found that the SWIR spectral parameters of chlorite,
white mica–montmorillonite and kandite group minerals have distinct
spatial variation across the Tonglushan skarn deposit, as described as
follows:
6.2. SWIR spectral parameters of chlorite
Chlorite occurs in many types of hydrothermal ore deposits and
low-/medium–grade metamorphic and sedimentary environments
(Vidal et al., 2001; Inoue et al., 2009). In SWIR spectrum, chlorite
group has diagnostic Fe–OH and Mg–OH absorption features centered
at ~2250 nm and ~2335 nm (i.e., Pos2250, Dep2250, Pos2335 and
Dep2335) (Fig. 9a; Jones et al., 2005; Biel et al., 2012). Based on the
spectral wavelength (nm) and TSG reference library, from low- to high
values of Pos2250 and Pos2335, chlorite can be divided into three sub-
groups, i.e., Mg-chlorite, Int-chlorite and Fe-chlorite (Fig. 9a; Jones
et al., 2005; Han et al., 2018).
At Tonglushan, chlorite was found in 1839 spectral data points
(23.3% of the total) from 924 rock samples, among which 468 spots
show chlorite-only, and the rest show mixing with montmorillonite, il-
lite, kaolinite and/or saponite (Table S1). The wavelength of Fe–OH and
Mg–OH absorption features covers the ranges of 2240.0–2266.1 nm and
2300.0–2369.1 nm (mostly 2244–2254 nm, mean = 2249.8,
S.D. = 4.9 nm, n = 1839) and 2320–2345 nm (mean = 2333.4,
S.D. = 9.6 nm, n = 1839), respectively (Fig. 10a–b). Fe–OH wavelength
absorption position (Pos2250) of chlorite shows an increasing trend close
to the skarns–hydrothermal center (alteration zone III) (Fig. 11a–b). To
reveal the actual spatial variation patterns, three drill holes (ZK406,
ZK803 and ZK006) were selected for SWIR spectral comparison
(Fig. 12a–c). Scatter diagrams show that the lower limit of Pos2250 (that
could indicate concealed orebodies) is ~2250 nm. Due to the varying
and complex contact metasomatic features, the longest indicative dis-
tance from the concealed orebodies is ca. 400 m (Fig. 12a–c). In addition,
due to the proximity to hidden intrusive contact and influence from the
retrograde alteration and chlorite-bearing veins, some abnormally high
Pos2250 values occur in the shallow and middle parts (alteration zone II)
of drill-holes ZK1203 and ZK803 (Fig. 11b). Unlike the Fe–OH absorption
features, the Mg–OH wavelength absorption position (Pos2335) of
chlorite shows less variation (ESM 1 Fig. A1).
6.3. SWIR spectral parameters of white mica–montmorillonite
White micas include phengite, illite, muscovite and paragonite, and
are ubiquitously found in many types of hydrothermal ore deposits
(Cooke et al., 2014; Mauger et al., 2016; Wang et al., 2017; Huang
et al., 2018). This mineral group has diagnostic Al–OH absorption
features centered at ~2,200 nm (i.e., Pos2200 and Dep2200)
(Herrmann et al., 2001; Jones et al., 2005). Since montmorillonite
(smectite group) has similar SWIR spectral features (1,900 and
2,200 nm) to white mica, IC value (illite crystallinity = Dep2200/
Dep1900) has also been widely used to evaluate the crystallinity of
white mica and montmorillonite (Herrmann et al., 2001; Yang et al.,
2012; Xu et al., 2017).
At Tonglushan, white mica and montmorillonite were identified in
3,635 spectral data points (46.0% of the total) from 1,430 rock samples,
among which 1,767 spots show only white mica–montmorillonite, and
the rest show a mixture with chlorite, kaolinite, dickite, calcite and/or
ankerite (Tables S2 and S3). The wavelength of Al–OH absorption
features and IC values are of 2,197.2–2,229.9 nm (mostly
2,206–2,212 nm, mean = 2,209.0, S.D. = 4.9 nm, n = 3635) and
0.03–2.62 (mostly 0.2–0.6, mean = 0.43, S.D. = 0.22, n = 3635),
respectively (Fig. 13a-b). SWIR spectral parameter of Al–OH wave-
length absorption position (Pos2200) of white mica–montmorillonite
shows a distinct change (Fig. 14a–b). In alteration zone I, most Pos2200
values change from 2,202 to 2,212 nm; while the values are higher
(Pos2200 > 2212 nm) in alteration zones II, III and IV (Fig. 14a-b).
Meanwhile, the abnormally lower Pos2200 values (Pos2200 <
2202 nm) also occur in alteration zone III (Fig. 14a-b). However, the IC
values of white mica–montmorillonite show less spatial variation (ESM
1 Fig. A2).
Fig. 10. Frequency distribution histogram of absorption band position (Pos) for
Fe–OH and Mg–OH absorption of chlorite. (a) Fe–OH absorption position; (b)
Mg–OH absorption position.
12

6.4. SWIR spectral parameters of kandite group
Kandite group minerals include kaolinite, dickite and halloysite, and
are usually formed in an acidic environment (Hemley And Jones, 1964;
Hedenquist et al., 2000; Cohen, 2011). At Tonglushan, kandite was
found in 1,131 spectral data points (14.3% of the total) from 566 rock
samples, among which 250 spots show only kandite, and the rest show
mixing with montmorillonite, chlorite, calcite, ankerite and/or dolo-
mite (Table S4). For the SWIR spectrum, the sub-Al–OH wavelength
absorption position (Pos2170) and half-width of Al–OH absorption
feature are important indicators for the crystallinity and temperature of
kandite group minerals (Cohen, 2011). In the 4# profile and cross-
section of A–A’, the Pos2170 values clearly increase close to alteration
zone III (Fig. 15a–b). The half-width of kandite Al–OH absorption fea-
tures is readily influenced by other minerals that contain Al–OH, such
as illite, montmorillonite and muscovite (Fig. 9b–d; Table S4), which
limits its use at Tonglushan.
7. Discussion
7.1. Implications from the phyllosilicate minerals zonation at Tonglushan
Alteration zonation of skarn deposits varying from micrometer
(intra-grain)-scale to kilometer (deposit)-scale. The zonation can trace
fluid flow, wall-rock reaction and hydrothermal fluid evolution, and
can also serve as exploration tools (Meinert et al., 1997, 2005). As for
the intra-grain scale, two or more mineral generation (notably for
garnet) with different structure and chemical compositions may record
a progressive reaction with infiltrating hydrothermal fluids in many
skarn deposits (Jamtveit, 1991; Jamtveit and Andersen, 1993; Smith
et al., 2004; Meinert et al., 2005). Moreover, the color and composition
of garnet may also indicate the distance to the intrusive contact (Chang
and Meinert, 2008). As for the ore deposit scale, a common spatial
zoning pattern in skarn deposits can help to vector toward the skarn
hydrothermal center. For instance, from the causative intrusion,
through endoskarn and exoskarn to the carbonate wallrocks, decreasing
garnet/pyroxene ratios and appearance of distal vesuvianite and
Fig. 11. Distribution features of chlorite Fe-OH wavelength absorption position (Pos2250) in the Tonglushan prospecting-line 4# and cross-section A–A’ at
Tonglushan.
13

wollastonite (and bustamite) (Meinert et al., 2005). Besides, distal al-
teration features, such as bleached marble, fluid escape structures and
isotopic halos can also be used as prospecting indicators (Meinert et al.,
2005).
Different from common skarn deposits, the newly discovered or-
ebodies at Tonglushan are the concealed ones hosted in (dolomitic)-
marble xenolithic blocks (Fig. 3; Hu et al., 2011; Zhang et al., 2018),
and thus the causative quartz monzodiorite (porphyry) may be affected
by distal alteration (Fig. 3). However, different from the F-rich mag-
matic–hydrothermal system with a developed endoskarn zone (Chang
and Meinert, 2004, 2008), the skarn/retrograde alteration in the Ton-
glushan quartz monzodiorite (porphyry) are relatively undeveloped
with only sporadic actinolite and serpentine alteration (Fig. 8a–b).
Therefore, limited alteration information and exploration indicators
could be obtained from this alteration zone.
In this study, a large number of phyllosilicate minerals (e.g.,
chlorite, white mica, smectite and kandite groups) are identified
throughout the Tonglushan mining area, especially chlorite, illite,
kaolinite and dickite in the upper “surrounding rocks” zone (Fig. 8c, d).
Their petrographic and SWIR spectral features indicate that most of
them are closely related to the medium- to low temperature alteration
at Tonglushan (Figs. 5 and 6). Moreover, the saponite distribution is
consistent with the skarn/retrograde alteration minerals, and kaolinite
and dickite are mainly present in the deeper parts of internal/external
intrusive contact (Fig. 8c–d). The presence of these phyllosilicate mi-
nerals can be taken as the direct indicators for the concealed skarn
orebodies at Tonglushan.
7.2. Hydrothermal fluid evolution of the Tonglushan skarn deposit
Published fluid inclusion studies reveal three types of inclusions,
i.e., liquid-rich, halite-bearing and vapor-rich ones, at Tonglushan
(Zhao et al., 2012a). The fluid inclusions in garnet, diopside, epidote,
quartz, K-feldspar and calcite homogenized at > 550 °C (S1),
400–570 °C (S2), 240–350 °C (S3), and 170–280 °C (S4), with the
corresponding salinities of > 65 wt%, 48–55 wt%, 5–50 wt% and
1–4 wt% NaCl eqv., respectively (Zhao et al., 2012a). This indicates
Fig. 12. Scatter diagram of distance from orebody vs. Fe–OH absorption feature
wavelength position (Pos2250) from drill cores at Tonglushan.
Fig. 13. Frequency distribution histogram of absorption band position (Pos)
and IC crystallinity for Al–OH absorption of white mica–montmorillonite. (a)
Al–OH absorption position; (b) IC crystallinity.
14

decreasing temperature and varying salinities during the Cu–Au ore
sulfides precipitation. Moreover, oxygen and hydrogen isotope data
show that the skarn formation (S1) was sourced from the magma-
tic–hydrothermal fluid, with certain meteoric water incursion during
the later ore (S2 and S3) and carbonate alteration (S4) stages (Zhao
et al., 2012a).
Common skarn/retrograde alteration minerals, e.g., garnet, diop-
side, actinolite, epidote, phlogopite, K-feldspar and biotite, indicate
that the hydrothermal fluids are dominantly alkaline-neutral with re-
latively high temperatures (e.g., Meinert et al., 2005; Peng et al., 2016).
However, different from many previous studies (e.g., Meinert et al.,
1997, 2005), we found abundant fine-grained, low-temperature phyl-
losilicate minerals at Tonglushan which may indicate neutral to acidic
hydrothermal fluids (Fig. 8c–d), notably kaolinite and dickite that are
common in high-sulfidation epithermal ore fluids (pH: 2–4; Hemley and
Jones, 1964; Hedenquist et al., 2000).
As described in Section 4, large amounts of Fe-oxides and Cu–Au-
sulfides were precipitated in stages S2 and S3, such as magnetite, he-
matite, specularite, chalcopyrite, bornite, chalcocite and pyrite (Fig. 4).
Similar to porphyry Cu (–Au) deposits, more H+
would be generated
with the Fe-oxide and sulfides precipitation (Eq. (1); Sun et al., 2013,
2015).
+ + + +
+ +
SO 12 Fe 12 H O 4 Fe O S 24 H
4
2 2
2 3 4
2
According to the experimental phase diagram (Fig. 16a), K-feldspar
mainly occurs under the conditions of quartz saturation, high tem-
perature-pressure (100 MPa) and K+
content (Fig. 16a). With de-
creasing temperature and K+
/H+
molar ratios, muscovite and/or
phengite were formed. Illite is also formed under relatively low tem-
perature conditions (Fig. 16a-b; Hemley, 1959; Sverjensky et al., 1991).
This agrees with the presence of white mica (muscovite, phengite and
illite) in mainly the quartz monzodiorite (porphyry), closely spatially
related to K-feldspar alteration (Fig. 8c-d).
With the hydrothermal fluid evolution, the H+
excess in the fluids
would impede the Fe-oxides and Cu–Au-sulfides precipitation (Eq. (1);
Meinert et al., 2005). On one hand, fluid neutralization occurs as H+
ions react with (dolomitic)-marble during the fluid ascent (Shu et al.,
2017), releasing CO2 and H2O (Eqs. (2) and (3)).
Fig. 14. Distribution features of white mica–montmorillonite Al–OH wavelength absorption position (Pos2200) in prospecting-line 4# and cross-section of A–A’ at
Tonglushan.
15

+ +
+ +
CaCO H HCO 3 Ca
3
2
+ +
+
HCO 2H H O CO
3 2 2
On the other hand, as H+
ions react with the shallow-level quartz
monzodiorite (porphyry), the feldspars in the latter would generate the
acidic kaolinite and dickite (Eq. (4); Hemley, 1959; Hemley and Jones,
1964).
4X[AlSi3O8] + 4H2O + 2CO2 ⇌ Al4[Si4O10](OH)8 + 8SiO2
+ 2X2CO3([4];X = K,Na,1/2Ca)
Similarly, in the (dolomitic)-marble, the CO2 and H+
produced
could react with the residual Si-Al components from the quartz dioritic
magma during contact metasomatism. This likely formed the acidic
kaolinite and dickite observed at the upper intrusive contact in the
concealed skarn orebodies at Tonglushan (Fig. 8c-d).
Therefore, we suggest that the majority of phyllosilicate minerals in
the deep parts of Tonglushan were derived from the low-temperature
hydrothermal fluids during the contact metasomatism and Cu–Au–Fe
skarn mineralization. We consider that the hydrothermal system was
originally (S1) characterized by having high temperature and high K+
content (Fig. 16a). With the evolution of hydrothermal fluids and ore
minerals precipitation (S2 to S3), the hydrothermal system transformed
gradually into medium-low temperature with lower K+
/H+
ratios
(Fig. 16a). As a consequence, the neutral-acidic hydrothermal fluids
likely reacted with the (dolomitic)-marble and feldspars to form phyl-
losilicate minerals, such as chlorite, illite, kaolinite and dickite
(Fig. 16a-b).
7.3. Mineral SWIR vectoring to concealed skarn orebodies at Tonglushan
Our SWIR spectral mapping has identified kaolinite, dickite and
saponite in the internal/external intrusive contact (alteration zones II
and IV) and skarn–hydrothermal center (alteration zone III) (Fig. 8c-d).
Besides, the chlorite–quartz–sulfides veins and actinolite/phlogopite-
bearing veins mainly occur in alteration zone II (Fig. 5 and 8a-b).
Spatially, they are more widely distributed than the common skarn/
retrograde alteration minerals and closer to the skarn–hydrothermal
center at Tonglushan (Fig. 8c-d). Thus, the presence of intensive kao-
linite, dickite, saponite, actinolite, phlogopite and/or chlor-
ite–quartz–sulfides veins can be used as vectoring tools for the
Fig. 15. Distribution features of kandite sub-Al–OH wavelength absorption position (Pos2170) in prospecting-line 4# and cross-section A–A’ at Tonglushan.
16

concealed skarn orebodies at Tonglushan.
Apart from these indicator minerals, chlorite, white mica–-
montmorillonite and kandite are also widespread at Tonglushan
(Fig. 8c-d). Chlorite was mainly formed in stage S3, including DC-
(alteration zones I and II), VC- (alteration zone II) and RC- (alteration
zone III) types (Fig. 4 and 8c-d). SWIR spectral analysis shows higher
Pos2250 values in the RC-type chlorite (2249.1–2260.6 nm, avg.
2257.3 nm) than in the VC-type chlorite (2244.0–2250.1 nm, avg.
2247.2 nm) (Table S1). Comparatively, the DC-type chlorite has rela-
tively wide Pos2250 range (2241.5–2253.5 nm, avg. 2248.0 nm) (Table
S1). In alteration zone III, high-Pos2250 DC-type chlorite is common in
the residual quartz monzodiorite (porphyry) (Fig. 11b). In this study,
the lower limit (~2250 nm) of Fe-OH absorption features (Pos2250) for
vectoring the concealed skarn orebodies were obtained, rather than a
linear relationship between Pos2250 and distance to the skarn–hy-
drothermal center (Fig. 12a–c).
Previous studies have shown that Fe–OH and Mg–OH absorption
features would both occur at longer wavelength (nm), and that the
chlorite would be richer in Fe (Jones et al., 2005; Han et al., 2018;
Huang et al., 2018). However, the Tonglushan chlorite Mg–OH wave-
length absorption position (Pos2335) is readily disturbed by other
Mg–OH-bearing minerals, such as phlogopite, saponite, talc, carbonate,
kaolinite and white mica (Fig. 9). The Tonglushan chlorite Pos2335
values thus show less variation (ESM 1; Fig. A1), and the chlorite
composition estimation and vectoring ability can only rely on the
Fe–OH absorption feature.
Apart from chlorite, white mica–montmorillonite Pos2200 also
shows an increasing trend toward the hydrothermal center (alteration
zones II, III and IV: > 2212 nm) (Fig. 14a–b). This phenomenon was
interpreted as the Alvi
(atoms per formula unit, a.p.f.u) in octahedral
position being replaced by other cations, e.g., Fe2+
and Mg2+
, which
would cause the Alvi
decrease but Pos2200 increase (Laakso et al.,
2016; Xu et al., 2017). At Tonglushan, the Alvi
in the octahedral posi-
tion may have been readily replaced by the Fe2+
and Mg2+
derived
from the Fe-/Mg-rich alteration minerals, such as garnet, diopside,
epidote and actinolite. Therefore, the high Pos2200 values of white
mica–montmorillonite are clustered around the Tonglushan skarn or-
ebodies (Fig. 14a–b).
In the quartz monzodiorite (porphyry) close to the intrusive contact,
some anomalously low Pos2200 values (< 2202 nm) were also found
(Fig. 14a-b). Previous studies show that Al–OH wavelength absorption
position (Pos2200) of white mica occurs at shorter wavelengths when
they are closer to porphyry- or VMS-type orebodies (Herrmann et al.,
2001; Jones et al., 2005; Yang et al., 2005; Yang et al., 2012; Harraden
et al., 2013; Huang et al., 2018). Generally, the white-mica Pos2200
values are negatively correlated to the Alvi
(a.p.f.u) contents in the
octahedral position and temperature (Duke, 1994; Scott and Yang,
1997; Wang et al., 2017). Due to the higher temperature near the hy-
drothermal center, white mica has higher Alvi
contents in the octahe-
dral position, corresponding to relatively low Pos2200 values (Scott and
Yang, 1997; Yang et al., 2012).
Different from typical porphyry Cu (–Au) deposits, the IC values of
white mica–montmorillonite are disorganized at Tonglushan (ESM 1
Fig. A2). The main reasons for that may have been: (i) many K-feldspar
(-quartz) veins and some high-temperature granite dykes that intruded
the quartz monzodiorite (porphyry) may contain minor muscovite with
high IC values; (ii) in the quartz monzodiorite (porphyry) near the in-
trusive contact, there may be mixed phyllosilicate minerals (e.g., white
mica, kaolinite and dickite) that have similar Al–OH absorption features
(ESM 1 Fig. A2; Table S2). Therefore, the IC value of white mica–-
montmorillonite is not applicable in this study.
At Tonglushan, kandite group minerals (esp. kaolinite and dickite)
are mainly distributed in the shallower parts of the intrusive contact,
with their spatial distributions mainly controlled by the contact zones
(Fig. 8c–d). Combined their petrographic and SWIR spectral features,
the majority of kaolinite and dickite samples collected at depth were
unlikely to be formed by weathering (Fig. 5r and 6r). The sub-Al–OH
absorption of kandite occurs at longer wavelengths (Pos2170 >
2,170 nm) in ore-proximal samples, and at shorter wavelengths
(Pos2170 < 2,170 nm) in ore-distal ones (Fig. 15a–b). This indicates
that the kandite has higher crystallinity and formation temperatures,
with higher Pos2170 values closer to the skarn orebodies. The presence
of kaolinite and dickite and the related SWIR spectral parameter
changes (Pos2170 > 2,170 nm) could effectively trace the intrusive
contact at depth, which helps to vector toward concealed skarn or-
ebodies at Tonglushan (Fig. 8c–d and 15a–b).
Based on the discussion above, we suggest that four indicators can
be used to vector toward concealed orebodies at Tonglushan, i.e., (i)
presence of kaolinite, dickite, saponite, actinolite, phlogopite and/or
chlorite–quartz–sulfides veins; (ii) high chlorite Pos2250 values
(> 2250 nm); (iii) unusual white mica–montmorillonite Pos2200 va-
lues (> 2212 nm and < 2202 nm); and (iv) high kandite Pos2170
values (> 2170 nm).
Fig. 16. (a) Stability of Al silicate minerals as a function of K+
/H+
molar ratios vs. temperature (at quartz saturation and 100 MPa; after Sverjensky et al., 1991;
Cohen, 2011); (b) Temperature and pH distributions of hydrothermal mineral assemblages at Tonglushan. Mineral stability data modified from Corbett and Leach
(1998). Abbreviations: And = andalusite, Pyroph = pyrophyllite, Dick = dickite, Kaol = kaolinite, Musc = muscovite, Pheng = phengite, Ill = illite,
Mnt = montmorillonite.
17

7.4. SWIR exploration potential comparison with other magmatic-
hydrothermal deposits
Variation of chlorite SWIR spectra have been reported in many VMS
deposits (Jones et al., 2005; Laakso et al., 2016): In the Myra Falls
(British Columbia) and Izok Lake (Nunavut) deposits in Canada, Arroyo
Rojo (Tierra del Fuego) deposit in Argentina, and Honghai (Eastern
Tianshan) deposit in China, the relatively Mg-rich chlorite with shorter
wavelength of Pos2250 were found close to the orebodies (Table S5;
Jones et al., 2005; Biel et al., 2012; Laakso et al., 2016; Huang et al.,
2018). For the majority of VMS deposits, Mg-rich chlorite are com-
monly identified in the ore-proximal zones (e.g., Urabe et al., 1983;
Gemmell and Large, 1992; Jones et al., 2005). This is interpreted as the
influx or replacement of seawater during the sulfides precipitation
(Hannington et al., 2003; Franklin et al., 2005; Huang et al., 2018).
A similar variation was also documented in some porphyry Cu (–Au)
deposits. For example, some workers found that the chlorite Fe–OH
wavelength absorption position (Pos2250) decreases toward the hy-
drothermal centers in the Batu Hijau deposit, Indonesia (Neala et al.,
2018). However, the opposite trend is also reported in the Paleozoic
Tuwu porphyry Cu deposit, NW China (Yang et al., 2005). The Fe-rich
chlorite with high Pos2250 values may reflect the inheritance of pre-
existing high-temperature biotite formed in/around the hydrothermal
centers, while the relatively Mg-rich chlorite in the ore-barren area may
represent the widespread propylitization products of the altered ba-
saltic-andesitic rocks (Yang et al., 2005).
At Tonglushan, the chlorite Pos2250 values show large variation
between the skarn–hydrothermal center (alteration zone III) and ore-
barren quartz monzodiorite (porphyry) (alteration zone I) (Fig. 11a-b).
In alteration zone III, chlorite mainly replaced epidote, garnet or
magnetite (Fig. 6o); whereas in alteration zone I, it mainly replaced
hornblende/biotite in the quartz monzodiorite (porphyry) (Fig. 5l, m).
Therefore, the original rocks/minerals, fluid composition and hydro-
thermal temperature may be the principal controlling factors on the
SWIR spectral parameters and chlorite chemical compositions.
Compared with chlorite, SWIR spectroscopy (esp. Al–OH absorption
features) of white mica is more widely used in porphyry- and VMS-type
deposits (e.g., Herrmann et al., 2001; Jones et al., 2005; Yang et al.,
2005; Table S5). Besides the ore-proximal shorter white mica Pos2200
wavelength feature (e.g., Jones et al., 2005; Harraden et al., 2013), the
longer wavelengths of Al–OH wavelength absorption position
(Pos2200) of the ore-proximal white mica have also been reported
(Laakso et al., 2016; Xu et al., 2017). Similar to the Tonglushan skarn
ore deposit, these SWIR features in the porphyry- and VMS-type de-
posits were interpreted as Fe2+
and Mg2+
replacing Alvi
(a.p.f.u) in the
octahedral position of white mica (Laakso et al., 2016; Xu et al., 2017).
In many porphyry Cu (–Au) deposits, the white mica (illite) crys-
tallinity (IC) decreases away from the hydrothermal center (e.g., Yang
et al., 2012; Xu et al., 2017). Under high-temperature conditions, the
tetrahedral position of illite is mainly occupied by (Al + K). With de-
creasing temperature, the (Al + K) contents are gradually replaced by
Si and vacancy, which would increase the H2O contents in the lattice
interlayer, leading to decreasing Dep1900 and increasing IC values
(Yang et al., 2012; Xu et al., 2017). The decreasing temperature away
from the porphyry-type hydrothermal centers makes the IC value an
effective indicator for exploring unknown hydrothermal centers
(Sillitoe, 2010; Xu et al., 2017). However, it is unsuitable for the Ton-
glushan skarn deposit as discussed above.
8. Conclusions
1. Based on petrographic observation and SWIR spectral mapping, five
mineralization/alteration stage, i.e., pre-ore alteration (S1), Fe mi-
neralization (S2), Cu-Au mineralization (S3), carbonate alteration
(S4) and supergene alteration (S5). Four skarn alteration zones
(with distinct phyllosilicate assemblages) from the intrusion to
wallrocks have been delineated in the Tonglushan Cu–Au–Fe skarn
deposit.
2. Large amount of white mica, chlorite and kandites with higher
crystallinity are identified in the deep mineralization parts at
Tonglushan. This indicaties that medium-low temperature and
neutral-acidic hydrothermal fluids were likely generated with the
Fe-oxides and sulfides precipitation.
3. SWIR spectral characteristics reveal that the high chlorite Pos2250
(> 2250 nm) and kandite Pos2170 (> 2170 nm), anomalously
high/low Pos2200 values of white mica–montmorillonite
(< 2202 nm or > 2212 nm), and appearance of kaolinite, dickite,
saponite, actinolite, phlogopite and/or chlorite–quartz–sulfides
veins, can be used as effective vectors toward concealed skarn or-
ebodies at Tonglushan.
Declaration of Competing Interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influ-
ence the work reported in this paper.
Acknowledgments
This study was financially supported by the Chinese National
Science Fund (41725009), the Chinese Academy of Sciences Strategic
Pilot Science and Technology Special (XDB18000000) and the Special
Public Welfare Scientific Research Fund Project by Ministry of Land and
Resources, China (201511035). We would like to thank Dr. Chao Xu
and Dr. Jianhan Huang at Guangzhou Institute of Geochemistry,
Chinese Academy of Sciences (GIG–CAS), China and Jiacheng Liu (a
PhD candidate) at Hong Kong University, China, for their technical
assistance and discussion with SWIR spectral analysis. This is con-
tribution No. IS-2844 from GIG–CAS.
Appendix A. Supplementary data
Supplementary data to this article can be found online at https://
doi.org/10.1016/j.oregeorev.2020.103516.
References
Bai, C., Zhao, K.D., Duan, D.F., Samake, B., Yang, S.Y., Wei, K.T., 2015. Mineralogical
characteristics and petrogenesis of lamprophyre dikes from the Tonglushan Fe–Cu
deposit. Hubei Province. Acta Petrol. Sin. 31, 769–783 (in Chinese with English ab-
stract).
Biel, C., Subías, I., Acevedo, R.D., Yusta, I., Velasco, F., 2012. Mineralogical, IR-spectral
and geochemical monitoring of hydrothermal alteration in a deformed and meta-
morphosed Jurassic VMS deposit at Arroyo Rojo, Tierra del Fuego. Argentina. J.
South Am. Earth Sci. 35, 62–73.
Chang, Y.F., Liu, X.P., Wu, Y.C., 1991. The copper–iron belt of the Middle and Lower
reaches of Yangtze River. Geological Publishing House, Beijing, pp 1–380 (in Chinese
with English abstract).
Chang, Z., Hedenquist, J.W., White, N.C., Cooke, D.R., Roach, M., Deyell, C.L., Garcia, J.,
Gemmell, J.B., McKnight, S., Cuison, A.L., 2011. Exploration tools for linked por-
phyry and epithermal deposits: Example from the Mankayan intrusion–centered
Cu–Au district, Luzon. Philippines. Econ. Geol. 106, 1365–1398.
Chang, Z., Meinert, L., 2004. Vermicular textures of quartz phenocrysts, endoskarn, and
implications for late stage evolution of granitic magma. Chem. Geol. 210, 149–171.
Chang, Z., Meinert, L., 2008. The Empire Cu–Zn Mine, Idaho: Exploration Implications of
Unusual Skarn Features Related to High Fluorine Activity. Econ. Geol. 103, 909–938.
Chang, Z., Shu, Q., Meinert, L.D., 2019. Skarn deposits of China: Society of Economic
Geologists. Special Publication 22, 189–234.
Chang, Z., Yang, Z., 2012. Evaluation of inter-instrument variations among Short
Wavelength Infrared (SWIR) devices. Econ. Geol. 107, 1479–1488.
Cohen, J.F., 2011. Compositional Variations in Hydrothermal White Mica and Chlorite
from Wall-Rock Alteration at the Ann-Mason Porphyry Copper Deposit, Nevada.
Master dissertation. Oregon State University, pp. 1–121.
Cooke, D.R., Baker, M.J., Hollings, P., Sweet, G., Chang, Z.S., Danyushevsky, L., Gilbert,
S., Zhou, T.F., White, N.C., Gemmell, J.B., Inglis, S., 2014. New Advances in
Detecting the Distal Geochemical Footprints of Porphyry Systems-Epidote Mineral
Chemistry as a Tool for Vectoring and Fertility Assessments. Econ. Geol. Special
Publication 18, 1–27.
Corbett, G.J., Leach, T.M., 1998. Southwest Pacific Rim Gold-Copper Systems: Structure,
18

Alteration, and Mineralization. Special Publications of the Society of Economic
Geologists, Special Publication, pp. 1–237.
Deng, X.D., Li, J.W., Zhou, M.F., Zhao, X.F., Yan, D.R., 2015. In-situ LA–ICPMS trace
elements and U-Pb analysis of titanite from the Mesozoic Ruanjiawan W–Cu–Mo
skarn deposit, Daye district. China. Ore Geol. Rev. 65, 990–1004.
Duan, D.F., Jiang, S.Y., 2017. In situ major and trace element analysis of amphiboles in
quartz monzodiorite porphyry from the Tonglushan Cu–Fe (Au) deposit, Hubei
Province, China: insights into magma evolution and related mineralization. Contrib.
Mineral. Petrol. 172 (36), 1–17.
Duke, E.F., 1994. Near infrared spectra of muscovite, Tschermak substitution, and me-
tamorphic reaction progress: Implications for remote sensing. Geology 22, 621–624.
Feng, Y., Xiao, B., Li, R., Deng, C., Han, J., Wu, C., Li, G., Shi, H., Lai, C., 2019. Alteration
mapping with short wavelength infrared (SWIR) spectroscopy on Xiaokelehe por-
phyry Cu-Mo deposit in the Great Xing’an Range. NE China. Ore Geol. Rev. 112,
103062.
Franklin, J.M., Gibson, H.L., Jonasson, I.R., Galley, A.G., 2005. Volcanogenic massive
sulfide deposits. Economic Geology 100th Anniversary 98, 523–560.
Gemmell, J.B., Large, R.R., 1992. Stringer System and Alteration Zones Underlying the
Hellyer Volcanic Hosted Massive Sulfide Deposit, Tasmania. Australia. Econ. Geol.
87, 620–649.
Han, J., Chu, G., Chen, H., Hollings, P., Sun, S., Chen, M., 2018. Hydrothermal alteration
and short wavelength infrared (SWIR) characteristics of the Tongshankou porphyr-
y–skarn Cu–Mo deposit, Yangtze craton. Eastern China. Ore Geol. Rev. 101, 143–164.
Hannington, M., Kjarsgaard, I., Galley, A., Taylor, B., 2003. Mineral-chemical studies of
metamorphosed hydrothermal alteration in the Kristineberg volcanogenic massive
sulfide district. Sweden. Miner. Deposita 38, 423–442.
Harraden, C.L., Mcnulty, B.A., Gregory, M.J., Lang, J.R., 2013. Short wave infrared
spectral analysis of hydrothermal alteration associated with the Pebble porphyry
copper–gold–molybdenum deposit, Iliamna. Alaska. Econ. Geol. 108, 483–494.
Hedenquist, J.W., Arribas, A.R., Gonzalez-Urien, E., 2000. Exploration for epithermal
gold deposits: Rev. Econ. Geol. 13, 245–277.
Hemley, J.J., 1959. Some mineralogical equilibria in the system K2O–Al2O3–SiO2–H2O.
Am. J. Sci. 257, 241–270.
Hemley, J.J., Jones, W.R., 1964. Chemical aspects of hydrothermal alteration with em-
phasis on hydrogen metasomatism. Econ. Geol. 59, 538–569.
Herrmann, W., Blake, M., Doyle, M., Huston, D., Kamprad, J., Merry, N., Pontual, S.,
2001. Short wavelength infrared (SWIR) spectral analysis of hydrothermal alteration
zones associated with base metal sulfide deposits at Rosebery and Western Tharsis,
Tasmania, and Highway-Reward. Queensland. Econ. Geol. 96, 939–955.
Hu, Q.L., Jin, S.G., Wei, K.T., Huang, Z.H., Zhu, J.D., Zhang, G.S., 2011. Deep Prospecting
Progress and Further Prospecting Direction of Tonglushan Orefield in Daye City.
Hubei Province. Resour. Environ. & Eng 25, 182–187.
Huang, J., Chen, H., Han, J., Deng, X., Lu, W., Zhu, R., 2018. Alteration zonation and
short wavelength infrared (SWIR) characteristics of the Honghai VMS Cu–Zn deposit,
Eastern Tianshan. NW China. Ore Geol. Rev. 100, 263–279.
Inoue, A., Meunier, A., Patriermas, P., Rigault, C., Beaufort, D., Vieillard, P., 2009.
Application of chemical geothermometry to low-temperature trioctahedral chlorites.
Clay Clay Miner. 57, 371–382.
Jamtveit, B., 1991. Oscillatory zonation patterns in hydrothermal grossular andradite
garnet, nonlinear dynamics in regions of immiscibility. Am. Mineral. 76, 1319–1327.
Jamtveit, B., Andersen, T., 1993. Contact metamorphism of layered shale-carbonate se-
quences in the Oslo rift: III. The nature of skarn-forming fluids. Econ. Geol. 88,
1830–1849.
Jones, S., Herrmann, W., Gemmell, J.B., 2005. Short wavelength infrared spectral char-
acteristics of the HW Horizon: Implications for exploration in the Myra Falls
Volcanic-Hosted Massive Sulfide Camp, Vancouver Island, British Columbia. Canada.
Econ. Geol. 100, 273–294.
Laakso, K., Peter, J.M., Rivard, B., White, H.P., 2016. Short–wave infrared spectral and
geochemical characteristics of hydrothermal alteration at the Archean Izok Lake
Zn–Cu–Pb–Ag volcanogenic massive sulfide deposit, Nunavut, Canada: Application in
exploration target vectoring. Econ. Geol. 111, 1223–1239.
Lei, X.F., Duan, D.F., Jiang, S.Y., Xiong, S.F., 2018. Ore-forming fluids and isotopic
(H–O–C–S–Pb) characteristics of the Fujiashan-Longjiaoshan skarn W-Cu–(Mo) de-
posit in the Edong District of Hubei Province. China. Ore Geol. Rev. 102, 386–405.
Li, J.W., Deng, X.D., Zhou, M.F., Liu, Y.S., Zhao, X.F., Guo, J.L., 2010. Laser ablation
ICP–MS titanite U-Th–Pb dating of hydrothermal ore deposits: A case study of the
Tonglushan Cu–Fe–Au skarn deposit, SE Hubei Province. China. Chem. Geol. 270,
56–67.
Li, J.W., Vasconcelos, P., Zhou, M.F., Deng, X.D., Cohen, B., Bi, S.J., Zhao, X.F., Selby, D.,
2014. Longevity of magmatic–hydrothermal systems in the Daye Cu–Fe–Au district,
eastern China with implications for mineral exploration. Ore Geol. Rev. 57, 375–392.
Li, J.W., Zhao, X.F., Zhou, M.F., Ma, C.Q., Souza, Z.S., Vasconcelos, P., 2009. Late
Mesozoic magmatism from the Daye region, eastern China: U-Pb ages, petrogenesis,
and geodynamic implications. Contri. Miner. Petro. 157, 383–409.
Li, R.L., Zhu, Q.Q., Hou, K.J., Xie, G.Q., 2012. Zircon U-Pb dating and Hf isotopic com-
positions of granite porphyry and rhyolite porphyry from Jingniu basin in the Middle-
Lower Yangtze River Belt and its geological significance. Acta Petrol. Sin. 28,
3347–3360 (in Chinese with English abstract).
Liu, J.S., Ma, Guang, Shu, G.L., 2005. Discovery of cryptoexplosive breccia type Cu (Au)
orebodies in Tonglushan skarn–type Cu–Fe deposit of Hubei Province and ore-
searching vista. Mineral Deposits 24, 527–536 (in Chinese with English abstract).
Mao, J., Xie, G., Duan, C., Pirajno, F., Ishiyama, D., Chen, Y., 2011. A tectono–genetic
model for porphyry–skarn–stratabound Cu–Au–Mo–Fe and magnetite–apatite de-
posits along Middle-Lower Yangtze River Valley, Eastern China. Ore Geol. Rev. 43,
294–314.
Mauger, A.J., Ehrig, K., Kontonikas-Charos, A., Ciobanu, C.L., Cook, N.J., Kamenetsky,
V.S., 2016. Alteration at the Olympic Dam IOCG–U deposit: insights into distal to
proximal feldspar and phyllosilicate chemistry from infrared reflectance spectro-
scopy. Australian J. Earth Sci. 63, 959–972.
McIntosh, S., 2010. The future of base metals exploration, in Looking to the future: what’s
next? AMIRA International, 8th Biennial Exploration Managers’ Conference, Yarra
Valley, Victoria, Proceedings Volume.
Meinert, L.D., Dipple, G.M., Nicolescu, S., 2005. World skarn deposits. Economic Geology
100th Anniversary Volume, 299–336.
Meinert, L.D., Hefton, K.K., Mayes, D., Tasiran, I., 1997. Geology, zonation, and fluid
evolution of the Big Gossan Cu–Au skarn deposit, Ertsberg district, Irian Jaya. Econ.
Geol. 92, 509–534.
Neala, L.C., Wilkinson, J.J., Mason, P.J., Chang, Z., 2018. Spectral characteristics of
propylitic alteration minerals as a vectoring tool for porphyry copper deposits. J.
Geochem. Explor. 184, 179–198.
Peng, H.J., Mao, J.W., Hou, L., Shu, Q.H., Zhang, C.Q., Liu, H., Zhou, Y.M., 2016. Stable
Isotope and Fluid Inclusion Constraints on the Source and Evolution of Ore Fluids in
the Hongniu-Hongshan Cu Skarn Deposit, Yunnan Province, China. Econ. Geol. 111,
1369–1396.
Scott, K.M., Yang, K., 1997. Spectral reflectance studies of white micas. CSIRO
Exploration and Mining Report 439R. Australia, Sydney, pp. 1–35.
Shu, Q., Chang, Z., Hammerli, J., Lai, Y., Huizenga, J.-M., 2017. Composition and evo-
lution of fluids forming the Baiyinnuo’er skarn Zn-Pb deposit, northeastern China:
insights from laser ablation ICP-MS study of fluid inclusions: Econ. Geol. 112,
1441–1460.
Shu, Q.A., Chen, P.L., Cheng, J.R., 1992. Geology of Iron–Copper Deposits in Eastern
Hubei Province. Metallurgic Industry Press, Beijing, pp 1–532 (in Chinese with
English abstract).
Sillitoe, R.H., 2010. Porphyry copper systems. Econ. Geol. 105, 3–41.
Smith, M.P., Henderson, P., Jeffries, T.E.R., Long, J., Williams, C.T., 2004. The rare earth
elements and Uranium in Garnets from the Beinn an Dubhaich Aureole, Skye,
Scotland, UK: Constraints on Processes in a Dynamic Hydrothermal System. J. Petrol.
45, 457–484.
Sun, W.D., Huang, R.F., Li, H., Hu, Y.B., Zhang, C.C., Sun, S.J., Zhang, L.P., Ding, X., Li,
C.Y., Zartman, R.E., Ling, M.X., 2015. Porphyry deposits and oxidized magmas. Ore
Geol. Rev. 65, 97–131.
Sun, W.D., Liang, H.Y., Ling, M.X., Zhan, M.Z., Ding, X., Zhang, H., Yang, X.Y., Li, Y.L.,
Ireland, T.R., Wei, Q.R., Fan, W.M., 2013. The link between reduced porphyry copper
deposits and oxidized magmas. Geochim. Cosmochim. Acta 103, 263–275.
Sun, Y.Y., Seccombe, P.K., Yang, K., 2001. Application of short-wave infrared spectro-
scopy to define alteration zones associated with the Elura zinc–lead–silver deposit,
NSW. Australia. J. Geochemical Explor. 73, 11–26.
Sverjensky, A.D., Hemley, J.J., D'angelo, W.M., 1991. Thermodynamic assessment of
hydrothermal alkali feldspar–mica–aluminosilicate equilibria. Geochim. Cosmochim.
Acta 55, 989–1004.
Thompson, A.J., Scott, K., Huntington, J.F., Yang, K., 2009. Mapping mineralogy with
reflectance spectroscopy: Examples from volcanogenic massive sulfide deposits. Rev.
Econ. Geol. 16, 25–40.
Tian, J., Zhang, Y., Cheng, J.M., Sun, S.Q., Zhao, Y.J., 2019. Short wavelength infra-red
(SWIR) characteristics of hydrothermal alteration minerals in skarn deposits:
Example from the Jiguanzui Cu–Au deposit, Eastern China. Ore Geol. Rev. 106,
134–149.
Urabe, T., Scott, S.D., Hattori, K., 1983. A comparison of footwall-rock alteration and
geothermal systems beneath some Japanese and Canadian volcanogenic massive
sulfide deposits. Econ. Geol. Monogr. 5, 345–364.
Vidal, O., Parra, T., Trotet, F., 2001. A thermodynamic model for Fe-Mg aluminous
chlorite using data from phase equilibrium experiments and natural pelitic assem-
blages in the 100° to 600°C, 1 to 25 kb Range. Am. J. Sci. 301, 557–592.
Wang, R., Cudahy, T., Laukamp, C., Walshe, J.L., Bath, A., Mei, Y., Young, C., Roache,
T.J., Jenkins, A., Roberts, M., Barker, A., Laird, J., 2017. White mica as a hyper-
spectral tool in exploration for the Sunrise dam and Kanowna belle gold deposits,
western Australia. Econ. Geol. 112, 1153–1176.
Wei, K.T., Li, X.Z., Zhang, X.L., 2007. The characteristics of Tonglushan Cu–Fe deposit
and its prospecting future. Resour. Environ. & Eng. 21, 41–56 (in Chinese with
English abstract).
Xie, G., Mao, J., Li, X., Duan, C., Yao, L., 2011a. Late Mesozoic bimodal volcanic rocks in
the Jinniu basin, Middle-Lower Yangtze River Belt (YRB), East China: Age, petro-
genesis and tectonic implications. Lithos 127, 144–164.
Xie, G., Mao, J., Zhao, H., Wei, K., Jin, S., Pan, H., Ke, F., 2011b. Timing of skarn deposit
formation of the Tonglushan ore district, southeastern Hubei Province, Middle-Lower
Yangtze River Valley metallogenic belt and its implications. Ore Geol. Rev. 43,
62–77.
Xu, C., Chen, H.Y., White, N.C., Qi, J.P., Zhang, L.J., Zhang, S., Duan, G., 2017. Alteration
and mineralization of Xinan Cu–Mo ore deposit in Zijinshan orefield, Fujian Province,
and application of short wavelength infra-red technology (SWIR) to exploration.
Mineral Deposita 36, 1013–1038 (in Chinese with English abstract).
Yang, K., Lian, C., Huntington, J.F., Peng, Q., Wang, Q., 2005. Infrared spectral re-
flectance characterization of the hydrothermal alteration at the Tuwu Cu–Au deposit,
Xinjiang. China. Miner. Deposita 40, 324–336.
Yang, Z.Y., Hou, Z.Q., Yang, Z.S., Qu, H.C., Li, Z.Q., Liu, Y.F., 2012. Application of short
wavelength infrared (SWIR) technique in exploration of poorly eroded porphyry Cu
district: A case study of Niancun ore district. Tibet. Mineral Deposits 31, 699–717 (in
Chinese with English abstract).
Zhai, Y.S., Xiong, Y.L., Yao, S.Z., Lin, X.D., 1996. Metallogeny of copper and iron deposits
in the Eastern Yangtse Craton, east-central China. Ore Geol. Rev. 11, 229–248.
Zhai, Y.S., Yao, S.Z., Lin, X.D., Zhou, X.R., Wan, T.F., Jin, F.Q., Zhou, Z.G., 1992.
Metallogeny of Fe–Cu–(Au) ore deposits in mid–lower Yangtze River. Geological
19

Publishing House, Beijing, pp. 1–235 (in Chinese).
Zhang, S., Chen, H., Shu, Q., Zhang, Y., Chu, G., Cheng, J., Tian, J., 2019. Unveiling
growth histories of multi-generational garnet in a single skarn deposit via newly-
developed LA–ICP–MS U-Pb dating of grandite. Gondwana Res. 73, 65–76.
Zhang, S.T., Chen, H.Y., Han, J.S., Zhang, Y., Chu, G.B., Wei, K.T., Zhao, Y.J., Cheng, J.M.,
Tian, J., 2018. Geochronology, geochemistry, and mineralization of quartz mon-
zodiorite and quartz monzodiorite porphyry in Tonglushan Cu–Fe–Au deposit,
Edongnan ore district, China. Geochimica 47, 240–256.
Zhao, H., Xie, G., Wei, K., Ke, Y., 2012a. Mineral compositions and fluid evolution of the
Tonglushan skarn Cu–Fe deposit, SE Hubei, east-central China. Inter. Geol. Rev. 54,
737–764.
Zhao, H.J., Mao, J.W., Xiang, J.F., Zhou, Z.H., Wei, K.T., Ke, Y.F., 2010. Mineralogy and
Sr–Nd–Pb isotopic compositions of quartz diorite in Tonglushan deposit. Hubei
Province. Acta Petrol. Sin. 26, 768–784 (in Chinese with English abstract).
Zhao, H.J., Xie, G.Q., Wei, K.T., Ke, Y.F., 2012b. Skarn Mineral and stable isotopic
characteristics of Tonglushan Cu–Fe deposit in Hubei Province. Geol. Rev. 58,
379–395 (in Chinese with English abstract).
Zhao, Y.M., Lin, W.W., 1990. Skarn Deposits of China. Geological Publishing House,
Beijing, pp 1–346 (in Chinese with English abstract).
Zhou, T., Wang, S., Fan, Y., Yuan, F., Zhang, D., White, N.C., 2015. A review of the
intracontinental porphyry deposits in the Middle-Lower Yangtze River Valley me-
tallogenic belt. Eastern China. Ore Geol. Rev. 65, 433–456.
Zhou, T.F., Fan, Y., Wang, S.W., White, N.C., 2017. Metallogenic regularity and me-
tallogenic model of the Middle-Lower Yangtze River Valley Metallogenic Belt. Acta
Petrol. Sin. 33, 3353–3372 (in Chinese with English abstract).
20

Articulo3

Recommended

Recommended

More Related Content

What's hot

What's hot (19)

Similar to Articulo3

Similar to Articulo3 (20)

Recently uploaded

Recently uploaded (20)

Articulo3