MINERALIZATION OF THE MARINSKOYE POLYCHRONOUS GOLD DEPOSIT OF THE ALLAH-YUN METALLOGENIC ZONE (SOUTHERN VERKHOYANSK REGION, NORTHEAST OF RUSSIA): TYPES, MATERIAL COMPOSITION, GEOCHEMISTRY
Fridovsky V.Yu.1*, Polufuntikova L.I.1, Tarasov Y.A.1, Kudrin M.V.
1Diamond and Precious Metal Geology Institute SB RAS, Yakutsk, Russia
Keywords: quartz, carbonates, sulfides, native metals, ore textures and structures, mineralogy and geochemistry, gold orogenic deposit Marinskoye, Allah-Yun zone
Abstract
This paper presents the results of a study conducted on the chemical composition of ores from the Marinskoye orogenic gold ore field, located in the Allakh-Yun metallogenic zone of the Okhotsk-Koryak metallogenic belt (South Verkhoyanye). The deposit developed in a suprasubduction setting over the course of three discrete stages of ore formation: the early-ore stage (the Tithonian of the Late Cretaceous), the late-ore stage (the Aptian of the Early Cretaceous), which was associated with the exhumation of early ore-bearing complexes, and the telescoping of the late mineralization into early and post-ore stages. The main ore-bearing vein mineral is quartz; less common minerals include Fe-dolomite, dolomite and sericite. Ore minerals: primary – pyrite; secondary – arsenopyrite, galena, sphalerite; rare – native gold, pyrrhotite, boulangerite, hessite, petzite, sylvanite, tsnigriite, chalcopyrite, electrum, tetrahedrite, freieslebenite, diaphorite, stephanite. Ores from the early ore-forming stage are composed of quartz–sericite–carbonate–pyrite, arsenopyrite–pyrite–quartz, gold–galena–carbonate and telluride–sulphotelluride–sulfosalt associations; the total sulphide content in the ores is 1-2%. The metasomatites contain sparse inclusions of cubic crystals of arsenic-bearing gold-bearing pyrite (CAs mean = 1.17±0.06 wt%, СAu mean = 3.4±0.3 g/t). The early vein association consists of quartz with significant impurities of Ni (up to 61 g/t) and Cd (up to 4.3 g/t) and a low content of REE (SREE = 0.5-1.2 g/t). The fineness of native gold ranges from 660 to 780‰. Hessite, silvanite and tsnigriitehave been described for the first time at the Marinskoye deposit. In ores from the late-ore stage of mineralization, quartz–pyrite, pyrite–quartz, gold–polysulfide–carbonate, and Ag–sulfosalt associations have been identified, with sulfide content increasing to 5%. Low-arsenic pyrite with a pentagonal-dodecahedral shape is characteristic of the wallrock and quartz-carbonate veins. REE concentrations in quartz reach 29.6 g/t, their distribution shows enrichment in light lanthanides (LREE/HREE = 13.4-13.8), and a low-amplitude positive Eu-anomaly (Eu/Eu* = 1.3-1.6). In grains and aggregates of low-grade gold (up to 600‰), electrum rims and veinlets are prominent. The post-ore stage of mineral formation consists of minerals belonging to the quartz-carbonate association. The established general and distinctive properties of the mineralogical and geochemical composition of the ores of a different age at the Marinskoye deposit are essential for evaluating metallogenic potential of the telescoped ores.
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