MSci Final Project seminar, THE ORIGIN AND ASSOCIATED MINERALIZATION OF ALLUVIAL GOLD: THE LEADHILLS DISTRICT,SCOTLAND.

1. THE ORIGIN AND ASSOCIATED
MINERALIZATION OF ALLUVIAL
GOLD: THE LEADHILLS
DISTRICT, SCOTLAND.
SHAUN ADAMS
M[Earth]Sci
SCHOOL
OF EARTH, ATMOSPHERIC
AND ENVIRONMENTAL SCIENCES.
THE UNIVERSITY OF MANCHESTER

2. CONTENTS
• BACKGROUND
• GEOLOGY
• MINERALISATION
• PREVIOUS GOLD EXPLORATION
• SAMPLING
• DATA PRESENTATION
• CONCLUSIONS

3. BACKGROUND - What?
AIMS
• Identify mineralizing processes
• Summarize the distribution of gold
• Identify economically viable sites for gold
extraction.
EXECUTION
• Assessing published geological, geochemical
and geophysical datasets, for an indication of
gold distribution..
• Executed a Geochemical survey, on local stream
sediments.
• Performed Microchemical analysis of gold
grain(s) found.

4. BACKGROUND - Why?
• Lead – mined from 13th
century to 1959.
• Gold – alluvial gold
extraction since the
sixteenth century.
• Nuggets as large as
0.98kg
• 118 ounces of Leadhills
gold- Scottish crown
jewels • Longcleugh - favored spot, with
gravels between the glacial till and
bedrock on river banks most amicable
gold hosts (Leake et al., 1998).
• Gold has been recorded to be
restricted to a 20cm layer at the base
of the glacial till (Leake et al., 1998).

5. BACKGROUND – Where?
Sub Division Of Scottish Terranes
Moine Thrust
NORTHERN
HIGHLANDS
Great Glen Fault
GRAMPIAN
HIGHLANDS
Highland
Boundary Fault
MIDLAND VALLEY
TERRANE
(MVS)
Iapetus Suture
SOUTHERN
UPLANDS
Southern TERRANE
Uplands Fault (SUT)

6. BACKGROUND – Where?
The Southern Uplands are subdivided into three fault
banded tectno-stratigraphic units: THE NORTHERN,
CENTRAL AND SOUTHERN BELTS (Peach and Horne
1899).

7. GEOLOGY- Study Area

8. MINERALISATION
The Leadhills and Wanlockhead
veins display two stages of
mineralization:
1st stage - is widespread consisting
of quartz with associated pyrite,
muscovite, albite and gold
precipitated into faulted and
brecciated Ordovician
greywackes.
Main stage - large scale lead-zinc-
copper-silver veins of the region
(Temple, 1956).

9. PREVIOUS EXPLORATION
• 4 main types and
1 sub-type Leake
et al., (1998)
SOURCES
• Type 1 and 1a - major
systems show WSW trend.
– PPK and KKF, age
doesn’t control
occurrence.
– Shear zone related
mineralisation
• Type 2 – NW trending
tertiary dykes
• Type 3 – detrital deposits
within ultra-mafic rocks.
• Type 4 – Permian red bed
associated, (Thornhill basin).

10. SAMPLE SITES
SEDIMENT SAMPLES
FROM 2 RIVER
SYSTEMS:
SYSTEM A
• Tracts A1-4
• PPF & KKF
• Leadhills Fault Zone
• Tertiary Dykes
• Pb veins
SYSTEM B
• Tracts B1-5
• PPF
• Fardingmullach fault
• Pb and Qtz veins

11. SAMPLING METHODS
‘PAYSTREAKS’ Zones of
rapid velocity transition –
where heavy minerals are
naturally deposited in the
river.
Suction pump Crowbar
Wet Sieves – divided the
sediment into 5 fractions
D>2000μm, C 2000-720μm,
B 720-500μm, A 500-180μm,
F<180μm.

12. RESULTS
• GRAIN SIZE DISTRIBUTIONS
• LITHOLOGICAL DESCRIPTIONS
• X-RAY FLUORESCENCE
– MAJORS
– MINORS
• ESEM IMAGES

13. RESULTS
• GRAIN SIZE DISTRIBUTIONS
• LITHOLOGICAL DESCRIPTIONS
• X-RAY FLUORESCENCE
– MAJORS
– MINORS
• ESEM IMAGES

14. GRAIN SIZE - System A
A1 A2
A1
A4
A3
A2
A3 A4

15. GRAIN SIZE - System B
100 100
B1 B2
CUMULATIVE FREQUENCY (%)
CUMULATIVE FREQUENCY (%)
10 10
1 1
0 500 1000 1500 2000 0 500 1000 1500 2000
GRAIN SIZE (um) GRAIN SIZE (um)
SS17 SS15 SS14 SS13 SS25 SS26 SS27
SS9 SS10 SS11 SS12 SS13 SS25 SS26 SS27
B3
B2
B4
B5
B1
100
100
B3 B4
CUMULATIVE FREQUENCY (%)
CUMULATIVE FREQUENCY (%)
10
10
1 1
0 500 1000 1500 2000 0 500 1000 1500 2000
GRAIN SIZE (um) GRAIN SIZE (um)
SS16 SS15 SS14 SS13 SS25 SS26 SS27 SS19 SS18 SS14 SS13 SS25 SS26 SS27

16. RESULTS
• GRAIN SIZE DISTRIBUTIONS
• LITHOLOGICAL DESCRIPTIONS
• X-RAY FLUORESCENCE
– MAJORS
– MINORS
• ESEM IMAGES

17. LITHOLOGY + XRF MAJORS
Tract A2
•Al-Si-Fe rich
• large concentration of
lithology B (metamorphics
and shales).
• Peaks in Pb, S and Ba in
the D fraction at ss7 and
ss9.
Tract B1
• Al-Si-Fe rich.
•Increase of Na correlates
with an increase in B
fraction from ss25-27.
• Higher concentrations of
Si and K then system A,
silica peaks correlate with
lithology A.
• Metals favour grain size
and show consistent
pattern for full tracts
(titanium).

18. KEY POINTS – Grain Size and
Lithology + XRF Majors.
System A
• Coarser fractions in A2 and A3 then A4.
• Rapid increase in grain size ss7 (500-2000μm).
• Large concentration of Low grade Metamorphics and Shales in
sediments.
• Lead, sulphur and Barium peaks at ss7- restricted to the 720-
2000μm fraction.
System B
• Increase in fraction (500-2000μm) from ss9-10 and ss11-12.
• ss17-15 - huge increase in 500-720μm fraction.
• ss19/20-14 – increase in 720-2000μm fraction.
• Higher concentrations of Si and K then system A, silica peaks
correlate with sandstone rich sediments (Portpatrick formation).
• Metals favour larger grain sizes

19. RESULTS
• GRAIN SIZE
• LITHOLOGICAL DESCRIPTIONS
• XRF
– MAJORS
– MINORS
• ESEM IMAGES

20. XRF MINOR- System A
Tract A1
• High concentrations
of Fe and Pb.
•Fe gradual increase
•Peak at ss4 (all)
•Diminish by ss5
Tract A2-4
•ss7 peak in Leadhills Base
Metals (ppb >50,000ppm),
gold path finder elements
excluding Arsenic.
•ss6 trough of all above,
increase to ss5.
Arsenic
•A4 – source of Arsenic
• diluted by A3 and A4
•Peak at ss8 <20ppm
Tract A2- minimum dashed line, A3 - large dashed, A4 – solid
•Nothing at ss7

21. XRF MINOR- System B
Tract B1
•System B - vastly depleted in Leadhills base metals in comparison to A.
Peak in Pb at ss10 close to the Pb vein, Zn and Cu exhibit contrasting
peaks from ss10-13
•Gold path finders – peak in unison at ss11 after quartz vein, peaks in As
and Cr at ss13 and contrasting peak of Sb at ss25. Small increase of Sb
after ss26 after the tertiary dyke.

22. XRF MINOR- System B
Tract B2-5
•Peak in Sb and
Pb at ss15.
•Correlative B4,5
trough of Pb
and Sb at ss18.
•Substantial
decrease in Sb
when all tracts
coalesce.
• The most
significant Pb
deposits - Tract
B5. B2,3
•Tracts contains
highest
concentrations
of Cd. Tract B3 + B4 - Block lines, Tract B2, B5 - Dashed

23. XRF- Glacial Till
•Correlate to 100000
stream sediment 60
10000
MAJOR
analysis – high 50
CONCENTRATION (ppm)
CONCENTRATION (ppm)
40 1000
concentrations of
CONCENTRATION (%)
30
Si and Al. 20
100
10 10
•High 0
Na Mg Al Si K 1 Ca Ti Fe Pb
concentrations of ELEMENT Pb Cu Zn Ag Cd
ELEMENT
Mn F
GREY RED
gold path finder GREY RED
100000
elements. MINOR
10000
•Grey – larger
CONCENTRATION (ppm)
concentration of 1000
Leadhills base 100
metals and gold
path finder 10
elements then 1
Red. Pb Cu Zn Ag Cd
ELEMENT
Mn Fe Sb Cr
GREY RED

24. RESULTS
• GRAIN SIZE DISTRIBUTIONS
• LITHOLOGICAL DESCRIPTIONS
• X-RAY FLUORESCENCE
– MAJORS
– MINORS
• ESEM IMAGES

25. ESEM IMAGES

26. CONCLUSIONS
• The initial mineralization of gold in the area has progressed
through episodes of demineralization, large scale glaciation and
redistribution by fluvial systems.
• The widespread nature of lead-zinc mining has created a smear,
resulting in the blurring out of precious metals and creating a
heavy skew on grain size distribution.
• XRF data indicates that System A is the more fertile system in
terms of bulk metal composition
• Leadhills base metals concentrate in the larger fractions - fracture
dimensions in rock, durability.
• A significant source for gold in the system is likely to be indicative
of glacial sediments.
• Other potential gold sources could relate to tertiary dykes (Leake
et al., 1998), or by the main stage mineralization redistributing
gold from the initial stage.
• The relatively high concentrations of As, in fluvial system B could
indicate that Au-As type mineralization as seen in the Glendinning
deposit (Baron and Parnell, 2005) is prevalent in the area.

27. POTENTIAL SITES FOR
GOLD MINERALISATION
• Vein gold – within the
Leadhills Shear Zone
upstream from ss7
•Remobilization of gold
from early veins in the
Leadhills area, by the main
stage mineralization that
formed the major Lead-
Zinc-Copper-Silver veins.
Gold associated with
Au-As mineralization in
quartz veins, elevated
Arsenic levels are the
main justification for this
which could potentially
be accommodated by
Portpatrick Formation
and glacial tills.

28. REFERENCES
Baron, M., Parnell, J. (2005), Fluid evolution in base metal sulphide
mineral deposits in the metamorphic basement rocks of southwest
Scotland an Northern Ireland, Geological Journal, V 40:1, Pp 3 - 21
Leake, R.C., Chapman, R.J., Bland, D.J., Stone, P., Cameron, D.G.,
Styles, M.T. (1998) The origin of alluvial gold in the Leadhills area of
Scotland: evidence from interpretation of internal chemical
characteristics. Journal of Geochemical Exploration, 63, 7-36.
Pattrick, R.A.D., Russell, M.J. (1989) Sulphur isotopic investigation of
Lower Carboniferous vein deposits of the British Isles. Mineralium
Deposita, 24, 148-153.
Peach, B. N., & Horne, J. (1899) The Silurian Rocks of Britain.Vol. I,
Scotland. Mere. Geol. Surv. U.K.
Temple, A.K. (1956) The Leadhills-Wanlockhead lead and zinc deposits.
Transactions of the Royal Society Edinburgh: Earth Sciences, 63, 85-
113.
Woodcock, N. H. & Strachan, R. (2000). Geological History of Britain and
Ireland. Oxford: Blackwell Science. pp19-36,112-123,

29. “One of the greatest discoveries a man makes,
one of his greatest surprises, is to find he can do
what he was afraid he couldn't.”
~ Henry Ford, 1901 ~