Geological setting, mineralogy, geochemistry and genesis of the Middle Archaean Kalyadi copper deposit, western Dharwar craton, southern India |
| |
| Authors: | D V Subba Rao S M Naqvi |
| |
| Institution: | (1) National Geophysical Research Institute, Uppal Road, Hyderabad-500007, India, IN |
| |
| Abstract: | The Kalyadi polymetallic copper deposit occurs within the Middle Archaean (≥3.0 Ga), medium-grade Kalyadi schist belt which
consists predominantly of ultramafic-mafic schists interbedded with chemogenic chert, detrital high Al-Mg schists and siliceous
schists. This sedimentary exhalative type (SEDEX type) ore-body is the only copper deposit hosted in cherts in the western
Dharwar craton. The Kalyadi supracrustal rocks are intruded by tonalite-trondhjemitic gneisses (ca. 3.0 Ga) and granite (ca.
2.6 Ga). The Kalyadi copper deposit is polygenetic in nature. The primary ores represented by disseminations of pyrite ± linneite
and chalcopyrite ± magnetite essentially along the bedding lamination of the metachert are referred to as the metamorphosed
chert-sulphide rhythmites of a primary stratiform type. The ore is of low-grade and records imprints of at least two events
of deformation. Pyrite is characterised by high-Co values (262–4524 ppm) and high–Co/Ni ratios (3.0–19.7). Rare earth element
patterns of the primary ores and the host metacherts are identical, characterised by La enrichment, absence of Eu anomalies
and flat to depleted HREE patterns with δ
34 S = −0.8‰. The secondary (remobilised) ores are structurally controlled occurring as veins and stringers discordant to the
bedding lamination or schistosity. The constituent ores are chalcopyrite-pyrite-pyrrhotite with minor pentlandite. These sulphides
with low-Co/Ni ratios (0.87–1.80), have either a strong positive or negative Eu anomaly and show slight HREE enrichment. The
δ
34 S value ranges from +2.64 to −4.29‰. It is interpreted that the primary stratiform ores and the cherts were derived from
volcanogenic hydrothermal fluids as syngenetic/chemical deposits in a deep sea environment. The secondary epigenetic mineralisation
is related to subsequent migmatisation, deformational events and granitic activity.
Received: 8 September 1995 / Accepted: 18 November 1996 |
| |
| Keywords: | |
| 本文献已被 SpringerLink 等数据库收录！ |
|
