Dating of gold-sulphide ore formation process in carboniferous

Transcription

Dating of gold-sulphide ore formation process in
carboniferous marbles
(Shaukhokh Ore Area (North Ossetia, Russia)
Volkova M.M., Kostitsyn Yu.A., Bychkov D.A. Borisov M.V.
Lomonosov Moscow State University; Vernadsky Institute of Geochemistry and Analytical Chemistry, RAS
Content
• Targets of research
• Geology of Shaukhokh Ore Area
• Rocks composition
• Methods
• Results
• Summary
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Dating of gold-sulphide ore formation process in marmorized carboniferous limestones
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Targets of Research:
•
Age of gold-sulphide ore formation process
•
Relationship between endogenous process
known in region and gold-sulphide ore
mineralization
Reference Object: Shaukhokh Ore Field (North Ossetia, Russia)
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Physical map of Caucasus
Geological Map of North Ossetia
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Geological Map of Shaukhokh Ore Field
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Rocks composition
Cу-10
Py
Cу-9
Cal
Py
Chl
Cal
Bt, Chl
Electron probe micro-analyzer “Jeol JSM-6480LV”
Mineral grains size is up to 70 µ
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Cy-9 sample
Major minerals*: dolomite, calcite
Minor minerals*: biotite, chlorite,
albite, sphen, pyrite, galenite
*electron microprobe analysis
Phase Areas
100
2.64%
Area %
80
60
81.2%
40
20
5.71%
0
Cal
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Dol
Silicates
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Cy-10 sample
Major mineral*: calcite
Minor minerals*: biotite, chlorite, albite,
quartz, apatite, pyrite, galenite,
pyrrhotine, silver telluride
*electron microprobe analysis
Phase Areas
100
90.88%
Area %
80
60
2.25%
40
20
2.21%
0
Cal
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Pl
Chl+Bt
8
Soft leaching method
•
Small pieces of rock were placed in 50 ml
vial with 15 % CH3COOH.
• Acetic acid allows to dissolve carbonate
matrix only.
•
Leach residue is silicate fraction.
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X-ray phase analysis
№
Fraction
Mineral composition
СУ-9 WR
Whole rock
Dolomite, Calcite, Clinochlore
СУ-9 M
Magnetic
Dolomite, Ankerite, Biotite, Clinochlore
СУ-9 NM
Nonmagnetic
Ankerite, Clinochlore, Muscovite
СУ-10 WR
Whole rock
Calcite, Muscovite, Clinochlore
СУ-10 M
Magnetic
Muscovite, Clinochlore
СУ-10 NM
Nonmagnetic
Clinochlore, Calcite, Muscovite
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Rb-Sr isochron diagram for Су-9 and Су-10
0.715
87Sr/86Sr
0.714
Су-9
0.713
Су-10
0.712
0.711
0.710
T = 157.2 ± 4.1 Ma
MSWD = 2.9
0.709
0.708
87Rb/86Sr
0.707
0.0
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0.5
1.0
1.5
2.0
2.5
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Isochron or mixing line?
0.716
87Sr/86Sr
0.715
0.714
0.713
0.712
0.711
0.710
0.709
0.708
1/Sr
0.707
0
0.005
0.01
87Sr/86Sr
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0.015
0.02
0.025
vs 1/ Sr diagram
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Summary
•
According the data obtained we can state that using of soft leaching method
allowed us to determine the age of gold-sulphide mineralization in marmorized
carboniferous limestones. Two parallel isochrones give the age of 157.2±4.1 Ma.
Initial 87Sr/86Sr ratios are 0.70931±10 and 0.70755±11 respectively.
•
The results of our experiment showed that soft leaching method provides full
dissolution of carbonate matrix without any change in silicate minerals structure.
The experiment did not lead to fractionation of Rb in regard to Sr. So that Rb-Sr
system reflects the time of gold-sulphide ore formation.
• Considering the results obtained, we have
reasons to suppose that gold-sulphide ore
formation process in Shaukhokh Ore Area
could be related to Jurassic diabase-picrite
dyke complex.
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Thank you for your attention!
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Dating of gold-sulphide ore formation process in carboniferous

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