Abstract

Chromian muscovite ("fuchsite") with up to 8.5% Cr 2 O 3 , uvarovite garnet (up to 13.7% ZnO), and chromian rutile (up to 3.3% Cr 2 O 3 ), are variously associated with chlorite, biotite, epidote, kyanite, and tourmaline, all Cr-bearing, in Lower Paleozoic quartzite, biotite schist, marble, and carbonated ultramafic rocks in Northwest Nelson, New Zealand. Sulfides and carbonates associated with the Cr-silicates and oxides include pyrite, galena, gersdorffite, pentlandite, and calcite, siderite, cerussite, magnesite, dolomite, and ankerite. Chromium mineralization of the host rocks takes the form of this seams, and broad zones tens of meters wide that parallel host-rock schistosity and exhibit varying intensities of green coloration. All the Cr-rich localities occur within 3-4 km of Early Cretaceous granitic plutons and are close to, or lie within major fault zones. Field relationships, mineral textures, rock associations, and composites indicated that the mineral paragneiss is metasomatic in origin, and the result of hydrothermal fluids from the granitic plutons interacting with ultramafic rocks or detrital chromite derived from them.

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