Genesis and occurrence of metalliferous sediment presented by Mr SADIKUl AHAMMAD

1. Genesis and Occurrence of
Metalliferous Sediment
2nd Module
Deep Sea Exploration
Presented By
Mr. Sadikul Ahammad
M.Sc. Marine Science Student
Dept. Of Marine Science,
School of Marine Sciences,
Bharathidasan University,Trichy-620024

2. Introduction
 Metalliferous sediments are unconsolidated deep-sea deposits that form in
volcanically active areas on the floor of oceans and seas. An admixture of
hydrothermal metal-bearing matter from the interior in the Earth’s crust was and
is being contributed to the ocean by submarine high-temperature springs and as a
result the abiogenic part of these sediments is enriched in Fe, in a number of trace
elements, in many places in Mn, and depleted in Al and Ti.
 Some criteria for distinguishing metalliferous sediments have been offered.
According to Boström (1973), metalliferous sediments have a ratio of
Fe/(Al+Fe+Mn) greater than 0.5, a ratio of Al/(Al+Fe+Mn) less than 0.3, and a ratio
of (Fe+Mn)/Al greater than 2.5. According to Strakhov (1976), metalliferous
sediments have a ratio of (Fe+Mn)/Ti greater than 25. Lisitzin et al. (1976)
considered that sediments that have 10% or more Fe in the abiogenic part and that
are depleted in Al and Ti are metalliferous.
 Metalliferous sediments, which contain more than 30% Fe, are also referred to as
"ore sediments"

3. Genesis of Metalliferous Sediment
 There are two possibilities for the genesis of recent "metalliferous sediments":
 1. Submarine exhalative, i.e., "hydrothermal", bound to recent tectonic
faulting. These sediments contain the metals as sulphides, partly oxidized. The
best known examples are the ore brines in the Red Sea.
 2. Products of diagenesis and repeated redeposition of siliceous sediments,
mainly of radiolarian oozes. These products are of about the same composition
as the rust type. They contain the metals as oxides. The elements in this type
can be subdivided in groups: autochthonous, i.e., elements fixed in compounds
formed in the same place as they are sedimented, and terrigenous, i.e.,
elements fixed in compounds resistant to terrestrial weathering and in clay
minerals.
 The more the diagenesis is advanced, the higher is the content of the
autochthonous group of elements (which comprises Mn, Cu, Zn, etc.).

4. Metalliferous sediments from the Indian
ocean
 Recent metalliferous sediments occur in the Indian Ocean in the area of the
Rodriguez Triple Junction (Fig. 1.1). Metalliferous sediments also occur along
the axes of the Central Indian Ridge, Southeast Indian Ridge, and Southwest
Indian Ridge and in some sites in the Maria Celesta and Argo fault zones.
 Typical mid-ocean spreading centers marked by well developed axial valleys are
developed in the Rodriguez Triple Junction area at the intersection of the
Central Indian Ridge, Southeast Indian Ridge, and Southwest Indian Ridge
 The spreading rate of the Central Indian Ridge near the triple junction is 5–6 cm
a–1, The spreading rate the Southeast Indian Ridge near the triple junction is
7.0 cm a–1and The Southwest Indian Ridge has a triangular form with a sharp
top and has a slow spreading rate of 1.6 cm a–1
 From Eocene time to the present the Southwest Indian Ridge has been
developed by the rapid eastward movement of the triple junction area.

5.  Detached magmatic chambers are believed to exist
in the area of the triple junction under each of the
three converging ridges.
 Before the high-temperature hydrothermal vents
were discovered in the Indian Ocean (Hashimoto et
al. 2001; Gamo et al. 2001) increased concentrations
of Mn, Fe, CH4, and He and hydrothermal plumes
were mapped in the areas of the Rodriguez Triple
Junction, Central Indian Ridge, and Southwest Indian
Ridge.
 Enrichment in Fe and Mn and depletion in Al and Ti
of the sediments in the area of the Rodriguez Triple
Junction and along the axis of the Central Indian
Ridge and the Southeast Indian Ridge were first
mentioned by Boström (1973).
 The distribution of the ratios of Al/(Al+Fe+Mn) (Fig.
1.44) in the sediments of the area and ratios lower
than 0.30 are evident and significant on his chart.

6. Types of Metalliferous Sediment Have
Been Identified
 The following types of metalliferous sediment have been found within the
field studied: carbonaceous, clayey-carbonaceous, carbonaceous-clayey, and
clayey.
 Carbonaceous metalliferous sediments occur at depths from 3050 to 3770 m.
The contents of CaCO3 are usually greater than 90% and up to 96%.
Carbonaceous-clayey and clayey carbonaceous metalliferous sediments occur
at depths of 3660 to 4210 m. CaCO3 contents in them range from 13 to 20%
and from 81 to 87% respectively.
 Clayey metalliferous sediments occur at depths greater than 4320 m. The
content of CaCO3 in them is usually insignificant, <1%, but may be as high as
8–10% in some places. The carbonaceous part of the sediments is composed of
coccoliths with an admixture of foraminiferal material and the content of
biogenic silica is low.

7.  In the non-carbonate part of the metalliferous sediments the Fe-hydroxides occur
in very small grains and aggregates, ferruginous globules, and clots of silt size
ferruginous clay and Fe-Mn micronodules are present in places. Fragments of
edaphogenic material composed of basalt up to 1 cm in size commonly occur,
fragments of Fe-Mn crusts and fragments of basalt glass are less common and the
amounts of pyroxene, basic plagioclase, biotite, quartz, and zeolite minerals are
insignificant.
 There are clay and feldspar minerals, quartz and an abundance of X-ray amorphous
matter in the <1 μm size fraction. Goethite and Fe-montmorillonite minerals,
which are typically present in metalliferous sediments in the Southeast Pacific, are
rare.
 Average contents of chemical elements in abiogenic matter of metalliferous and
background sediments from the area of the Rodriguez Triple Junction are shown in
Table 1.5. The contents of Fe, Mn and most of the trace elements in metalliferous
sediments from the Indian Ocean are considerably lower than their contents in
metalliferous sediments from the Southeast Pacific, and the contents of Al, Ga, Ti,
and Cr are higher. The lower average rate of excessive accumulation of Fe, 1.2 mg
cm–2 ka–1, in metalliferous sediments from the Indian Ocean than in metalliferous
sediments from the Southeast Pacific, 5.5 mg cm–2 ka–1, indicates considerably less
intensive accumulation of hydrothermal matter in metalliferous sediments from the
Indian Ocean.

9. Element Carrier in Metalliferous Sediment
 The study of sediment cores has shown that in the area of the Rodriguez Triple
Junction the Quaternary metalliferous sediments are less distributed than the Late
Pliocene metalliferous sediments in which the excessive accumulation of elements
is greater.
 Accumulation rates of lithogenic material in the sediments of both ages are similar
and it is evident that accumulation rate of hydrothermal metal-bearing matter in
the studied Late Pliocene metalliferous sediments is higher.
 The relative roles of hydrothermal carriers of Fe, Mn, Cu, Zn, and V in the
Quaternary metalliferous sediments are considerably lower than in the Late
Pliocene metalliferous sediments. The relative roles of hydrothermal carriers of Ni,
Co, and Zr are similar in the Quaternary and Late Pliocene metalliferous sediments
(Fig. 1.48). The role of hydrothermal carriers of the elements in the Quaternary
metalliferous sediments to the east of the Rodriguez Triple Junction is higher than
in the sediments to the west of it. This obviously results from the easterly flowing
bottom currents.

11.  Fe- and Mn-oxyhydroxides play a greater role as element carriers in the Late
Pliocene metalliferous sediments than in the Quaternary metalliferous
sediments and much less than in metalliferous sediments from the Southeast
Pacific(Fig. 1.49).
 Unlike the metalliferous sediments from the Southeast Pacific, crystallized Fe-
oxyhydroxide minerals are prevalent minerals of Fe in the metalliferous
sediments from the Indian Ocean and are more abundant in the Late Pliocene
than in the Quaternary metalliferous sediments. About a half of the leachable
Cu, Zn, V, and Zr in the Quaternary metalliferous sediments and most of the
contents of these elements and about a half of the leachable Y in the Late
Pliocene metalliferous sediments are bound in crystallized Fe-oxyhydroxide
minerals. A predominant part of the leachable Ni, Co, and Y is bound with
amorphous Fe-hydroxides and Mn-oxyhydroxides in the Quaternary metalliferous
sediments and a predominant part of the Ni and Co is bound in these carriers in
the Late Pliocene metalliferous sediments.

12. Because of the lower sedimentation rate
the role of the crystallized Feoxyhydroxide
minerals as carriers of the trace elements
is higher in metalliferous sediments from
the Indian Ocean than in metalliferous
sediments from the Southeast Pacific. The
average sedimentation rate for
metalliferous sediments in the Indian
Ocean is about 1 mm ka–1, and is 3–5 mm
ka–1 for metalliferous sediments in the
Southeast Pacific.

13. Thank You!