Early Cretaceous Cortlandite-Pyroxenite-Gabbro Association of the Upper Amur Region: Geochronological and Geochemical Data

摘要

The Dambukin block of the Stanovoi terrane encloses abundant small (up to 5 km~2) massifs, dikes, and sills composed of the cortlandite-pyroxenite-gab-bro association. Previously, they were arbitrarily considered as Early Archean and Early Proterozoic formations. The dikes and sills are 1-2 km long and a few dozen meters thick. The association is largely represented by mesocratic and melanocratic gabbro, hornblendites, pyroxenites, cortlandites (hornblende peridotites), and less common dunites. In addition, phlogopite and pargasite (hornblende) are characteristic of cortlandites, while brownish green hornblende is typical of gabbroids. Pyroxenites and hornblendites occur frequently together in a single intrusion. Cortlandite and pyroxenite sills and dikes contain Pt-bearing Cu-Ni mineralization. Syngenetic disseminated and epige-netic (vein, brecciated, and massive) varieties are remarkable among Cu-Ni sulfide ores.