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Geochemical signatures of mesothermal Au-mineralized late-metamorphic deformation zones, Otago Schist, New Zealand

Geochemical signatures of mesothermal Au-mineralized late-metamorphic deformation zones, Otago Schist, New Zealand
Geochemical signatures of mesothermal Au-mineralized late-metamorphic deformation zones, Otago Schist, New Zealand
Hydrothermal processes along two regional-scale shear zones in the Otago Schist were dominated by structurally controlled fluid flow and mineralization in the host schist, with relatively minor quartz vein formation, and mineralized rocks are only subtly different from unmineralized rocks. Most Au in the shear zones is associated with sulphide minerals (pyrite and arsenopyrite) disseminated through the host schist or along microshears. Minor enrichment of Sb, Mo and Bi (ppm level) is detectable in the Hyde-Macraes Shear Zone (HMSZ). Hydrothermal muscovite is slightly more aluminous (1–2 wt%) than metamorphic muscovite in both shear zones. HMSZ muscovite averages >900 ppm N, in contrast to metamorphic muscovite that averages c. 200 ppm N. In both shear zones, rutile has replaced metamorphic titanite and epidote has altered to carbonate and phyllosilicates, but these reactions were nearly isochemical. Structurally controlled hydrothermal graphite in the HMSZ occurs in microshears (up to 3 wt%, above background <0.2 wt%). Alteration in the Rise & Shine Shear Zone (RSSZ) was accompanied by addition of abundant ankerite. The two shear zones have subtly different geochemical signatures and are not directly genetically related. However, As enrichment is a key exploration target for both shear zones.
mesothermal, orogenic, hydrothermal, arsenic, graphite, ankerite
1467-7873
225-232
Craw, D.
0479338f-1550-4606-9f73-bcdeffe71d38
MacKenzie, D.J.
73617310-f617-458e-92a0-5ae68255d849
Pitcairn, I.K.
fc7fc820-5cd9-4070-9623-23325563bc9f
Teagle, D.A.H.
396539c5-acbe-4dfa-bb9b-94af878fe286
Norris, R.J.
da11d4ba-dfed-429c-badf-b9825eb544c2
Craw, D.
0479338f-1550-4606-9f73-bcdeffe71d38
MacKenzie, D.J.
73617310-f617-458e-92a0-5ae68255d849
Pitcairn, I.K.
fc7fc820-5cd9-4070-9623-23325563bc9f
Teagle, D.A.H.
396539c5-acbe-4dfa-bb9b-94af878fe286
Norris, R.J.
da11d4ba-dfed-429c-badf-b9825eb544c2

Craw, D., MacKenzie, D.J., Pitcairn, I.K., Teagle, D.A.H. and Norris, R.J. (2007) Geochemical signatures of mesothermal Au-mineralized late-metamorphic deformation zones, Otago Schist, New Zealand. Geochemistry: Exploration, Environment, Analysis, 7 (3), 225-232. (doi:10.1144/1467-7873/07-137).

Record type: Article

Abstract

Hydrothermal processes along two regional-scale shear zones in the Otago Schist were dominated by structurally controlled fluid flow and mineralization in the host schist, with relatively minor quartz vein formation, and mineralized rocks are only subtly different from unmineralized rocks. Most Au in the shear zones is associated with sulphide minerals (pyrite and arsenopyrite) disseminated through the host schist or along microshears. Minor enrichment of Sb, Mo and Bi (ppm level) is detectable in the Hyde-Macraes Shear Zone (HMSZ). Hydrothermal muscovite is slightly more aluminous (1–2 wt%) than metamorphic muscovite in both shear zones. HMSZ muscovite averages >900 ppm N, in contrast to metamorphic muscovite that averages c. 200 ppm N. In both shear zones, rutile has replaced metamorphic titanite and epidote has altered to carbonate and phyllosilicates, but these reactions were nearly isochemical. Structurally controlled hydrothermal graphite in the HMSZ occurs in microshears (up to 3 wt%, above background <0.2 wt%). Alteration in the Rise & Shine Shear Zone (RSSZ) was accompanied by addition of abundant ankerite. The two shear zones have subtly different geochemical signatures and are not directly genetically related. However, As enrichment is a key exploration target for both shear zones.

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More information

Published date: August 2007
Keywords: mesothermal, orogenic, hydrothermal, arsenic, graphite, ankerite

Identifiers

Local EPrints ID: 65998
URI: https://eprints.soton.ac.uk/id/eprint/65998
ISSN: 1467-7873
PURE UUID: eb37fef0-57d6-4af2-81b7-369c208c1af3
ORCID for D.A.H. Teagle: ORCID iD orcid.org/0000-0002-4416-8409

Catalogue record

Date deposited: 17 Apr 2009
Last modified: 06 Jun 2018 12:52

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