PGE mineralization in the late Archaean iron-rich mafic-ultramafic Hanumalapur Complex, Karnataka, India |
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| Authors: | T T Alapieti T C Devaraju R J Kaukonen |
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| Institution: | (1) Department of Geosciences, University of Oulu, Oulu, Finland;(2) Department of Studies in Geology, Karnatak University, Dharwad, India |
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| Abstract: | Summary An unusually thick sulfur-poor mineralized zone enriched in platinum-group elements (PGE) is described in the Hanumalapur
Complex, Shimoga District, Karnataka State, India. This promising occurrence was discovered in the early 1990s and the best
samples at the time of writing have yielded Pt+Pd concentrations in excess of six ppm.
The western part of the area concerned belongs to the late Archaean Dharwar Super Group (3000–2500 Ma), while the eastern
part is occupied predominantly by a granite-gneiss terrain ∼3000 Ma in age. Ten mafic-ultramafic complexes which host interesting
vanadium-bearing titanomagnetite occurrences are encountered in the western part, one of which is the Hanumalapur Complex.
The PGE mineralized zone in this complex may be divided into four mineralogically distinctive types, which are, in descending
order of PGE content: 1) a silicate-hosted Pd type, 2) a silicate-hosted Pt type, 3) a base-metal sulfide-hosted Pd type,
and 4) an oxide-hosted PGE type.
The genesis of the mineralization is somewhat unclear at this point of investigation, especially because of complete re-crystallization,
but the evidence gathered so far suggests something different than a traditional orthomagmatic model requiring magma mixing
processes and resulting in sulfide immiscibility. This is backed-up by the general lack of base metal sulfides in favor of
chromite, although pure chlorite-amphibole and chlorite-albite-epidote-amphibole rocks may contain significant PGE concentrations
regardless of the amount of chromite. The PGM textures show little evidence of hydrothermal alteration and remobilization,
but the PGE mineralogy itself displays some characteristics of fluid action, as it seems that there are some OH-bearing Pt
and Pd minerals present.
The first author was Deceased
Author’s address: R. J. Kaukonen, Department of Geosciences, University of Oulu, Oulu, P.O. Box 3000, FIN-90014 Finland |
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