Reid Legere, MSc

K-feldspar is common in igneous rocks, wall rocks and in mineral deposits. Hydrothermal K-feldspar (adularia) is one of the essential components of epithermal gold veins. This study examines the occurrence and compositions of adularia from several mines and prospects in the Russian Far East region to evaluate the usefulness of adularia as a vector for mineralization. Samples are from the Kupol (180.7 t Au, 1986 t Ag), Dukat (40 t Au, 17 kt Ag), Dvoinoye (36.3t Au, 50.5t Ag) Kubaka (>100t Au, >100t Au), and Karamken mines, as well as satellite and prospective deposits. Cretaceous Okhotsk-Chukotka volcanic belt hosts these deposits except for the ~ 300 Ma Kubaka deposit in the Omolon massif.

All samples show banded Qz-adularia, with adularia occurring as coarse (>2mm) sub-rhombic to fine rhombic crystals (<50µm), crystal aggregates and cementations, in crustiform, colloform and brecciated veins as well as in wall rock replacing plagioclase. Adularia observed compositionally close to the end member orthoclase. Adularia often creamy to pale white is easily identified by cobaltinitrite staining. Fine rhombic adularia grains were the predominant style of adularia in samples and are commonly Ba-bearing (0.3-2.9wt% Ba), adjacent to bands of microcrystalline quartz and observed in close spatial association with electrum, Ag-tellurides, Ag-sulfosalts and sulphides, suggesting contemporaneous formation of adularia and precious metals.  Coarse sub-rhombic adularia contains various minerals including earlier albite, calcite, sulphides, sulfates and oxides. Pyrite has variably zoned compositions including arsenian pyrite (4.9-3.2 wt% As) and Co-bearing pyrite (0.6 wt% Co). Bladed calcite as well as Mn-bearing calcite were observed in certain samples. Mn-bearing minerals (rhodochrosite, rhodonite) are abundant in later ore at Dukat, with distinct pink band of rhodochrosite and rhodonite, with wispy rhodochrosite crosscutting coarse adularia containing earlier albite which also surrounds piemontite inclusions.

Future trace element analysis planned for this study aims to continue to assess the composition of adularia and its potential as a useful vector for Au-Ag mineralization in epithermal systems.