THE ORIGIN AND ASSOCIATED
MINERALIZATION OF ALLUVIAL
   GOLD: THE LEADHILLS
    DISTRICT, SCOTLAND.
         SHAUN ADAMS

...
CONTENTS
 • BACKGROUND

 • GEOLOGY

 • MINERALISATION

 • PREVIOUS GOLD EXPLORATION

 • SAMPLING

 • DATA PRESENTATION

 •...
BACKGROUND - What?
 AIMS

 • Identify mineralizing processes
 • Summarize the distribution of gold
 • Identify economicall...
BACKGROUND - Why?
• Lead – mined from 13th
century to 1959.

• Gold – alluvial gold
extraction since the
sixteenth century...
BACKGROUND – Where?
Sub Division Of Scottish Terranes
                                Moine Thrust

                      ...
BACKGROUND – Where?
The Southern Uplands are subdivided into three fault
banded tectno-stratigraphic units: THE NORTHERN,
...
GEOLOGY- Study Area
MINERALISATION
The Leadhills and Wanlockhead
   veins display two stages of
   mineralization:
1st stage - is widespread c...
PREVIOUS EXPLORATION
• 4 main types and
  1 sub-type Leake
  et al., (1998)


                     SOURCES
               ...
SAMPLE SITES
SEDIMENT SAMPLES
FROM 2 RIVER
SYSTEMS:


SYSTEM A
• Tracts A1-4
• PPF & KKF
• Leadhills Fault Zone
• Tertiary...
SAMPLING METHODS
                                 ‘PAYSTREAKS’ Zones of
                                 rapid velocity tr...
RESULTS
• GRAIN SIZE DISTRIBUTIONS
• LITHOLOGICAL DESCRIPTIONS
• X-RAY FLUORESCENCE
 – MAJORS
 – MINORS
• ESEM IMAGES
RESULTS
• GRAIN SIZE DISTRIBUTIONS
• LITHOLOGICAL DESCRIPTIONS
• X-RAY FLUORESCENCE
 – MAJORS
 – MINORS
• ESEM IMAGES
GRAIN SIZE - System A
A1                        A2




     A1
          A4


               A3
                    A2


A...
GRAIN SIZE - System B
                           100                                                                      ...
RESULTS
• GRAIN SIZE DISTRIBUTIONS
• LITHOLOGICAL DESCRIPTIONS
• X-RAY FLUORESCENCE
 – MAJORS
 – MINORS
• ESEM IMAGES
LITHOLOGY + XRF MAJORS
Tract A2
•Al-Si-Fe rich
• large concentration of
lithology B (metamorphics
and shales).
• Peaks in ...
KEY POINTS – Grain Size and
Lithology + XRF Majors.
System A

• Coarser fractions in A2 and A3 then A4.
• Rapid increase i...
RESULTS
• GRAIN SIZE
• LITHOLOGICAL DESCRIPTIONS
• XRF
 – MAJORS
 – MINORS
• ESEM IMAGES
XRF MINOR- System A
Tract A1
• High concentrations
of Fe and Pb.
•Fe gradual increase
•Peak at ss4 (all)
•Diminish by ss5
...
XRF MINOR- System B
Tract B1
•System B - vastly depleted in Leadhills base metals in comparison to A.
Peak in Pb at ss10 c...
XRF MINOR- System B
Tract B2-5
•Peak in Sb and
Pb at ss15.
•Correlative                                                   ...
XRF- Glacial Till
•Correlate to                                                                                           ...
RESULTS
• GRAIN SIZE DISTRIBUTIONS
• LITHOLOGICAL DESCRIPTIONS
• X-RAY FLUORESCENCE
 – MAJORS
 – MINORS
• ESEM IMAGES
ESEM IMAGES
CONCLUSIONS
•   The initial mineralization of gold in the area has progressed
    through episodes of demineralization, la...
POTENTIAL SITES FOR
GOLD MINERALISATION
• Vein gold – within the
Leadhills Shear Zone
upstream from ss7
•Remobilization of...
REFERENCES
Baron, M., Parnell, J. (2005), Fluid evolution in base metal sulphide
   mineral deposits in the metamorphic ba...
“One of the greatest discoveries a man makes,
one of his greatest surprises, is to find he can do
what he was afraid he co...
Upcoming SlideShare
Loading in …5
×

Shaun Adams

1,048 views
819 views

Published on

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

Published in: Technology
0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total views
1,048
On SlideShare
0
From Embeds
0
Number of Embeds
11
Actions
Shares
0
Downloads
7
Comments
0
Likes
0
Embeds 0
No embeds

No notes for slide

Shaun Adams

  1. 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. 2. CONTENTS • BACKGROUND • GEOLOGY • MINERALISATION • PREVIOUS GOLD EXPLORATION • SAMPLING • DATA PRESENTATION • CONCLUSIONS
  3. 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. 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. 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. 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. 7. GEOLOGY- Study Area
  8. 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. 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. 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. 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. 12. RESULTS • GRAIN SIZE DISTRIBUTIONS • LITHOLOGICAL DESCRIPTIONS • X-RAY FLUORESCENCE – MAJORS – MINORS • ESEM IMAGES
  13. 13. RESULTS • GRAIN SIZE DISTRIBUTIONS • LITHOLOGICAL DESCRIPTIONS • X-RAY FLUORESCENCE – MAJORS – MINORS • ESEM IMAGES
  14. 14. GRAIN SIZE - System A A1 A2 A1 A4 A3 A2 A3 A4
  15. 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. 16. RESULTS • GRAIN SIZE DISTRIBUTIONS • LITHOLOGICAL DESCRIPTIONS • X-RAY FLUORESCENCE – MAJORS – MINORS • ESEM IMAGES
  17. 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. 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. 19. RESULTS • GRAIN SIZE • LITHOLOGICAL DESCRIPTIONS • XRF – MAJORS – MINORS • ESEM IMAGES
  20. 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. 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. 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. 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. 24. RESULTS • GRAIN SIZE DISTRIBUTIONS • LITHOLOGICAL DESCRIPTIONS • X-RAY FLUORESCENCE – MAJORS – MINORS • ESEM IMAGES
  25. 25. ESEM IMAGES
  26. 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. 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. 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. 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 ~

×