Orogenic gold and rare metal deposits of the Upper Kolyma District, Northeastern Russia: Relation to igneous rocks, timing, and metal assemblages

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• 作者：S.V. Voroshin^a ; ¹ ; ^{voroshinsv@gmail.com" class="auth_mail} ; E.E. Tyukova^a ; ² ; R.J. Newberry^b ; P.W. Layer^b
• 关键词：Orogenic gold deposit ; Au-quartz vein ; Granitoid-related Au ; 40Ar/39Ar dating ; Arsenopyrite assemblages
• 刊名：Ore Geology Reviews
• 出版年：October 2014
• 年：2014
• 卷：62
• 期：Complete
• 页码：1-24
• 全文大小：6031 K

文摘

The Upper Kolyma district is the most important part of the Yana–Kolyma gold province, administratively located in Magadan Oblast, Russia. To date, historic production of the region is about 90 Moz of gold, mostly from placers, but with about 5% contribution from lode deposits. Two major types of gold deposits are distinguished in the region: (1) Au-quartz veins related to regionally metamorphosed rocks; and (2) granitoid-related Au. Besides gold, tin deposits are also wide-spread and can be distinguished as: (1) Sn-quartz veins, (2) Sn-silicate-sulfide veins, and (3) Sn-polymetallic veins. Quartz-molybdenite (porphyry Mo) and Ag-polymetallic (Ag-quartz) veins are less abundant. Metamorphic zones and major regional faults are the most important factors of control for the Au-quartz veins. Granitoid intrusions are the most important ore-controlling factor for other deposit types.

Field relationships between Au-quartz vein, granitoid-related Au mineralization and intrusions, as well as the ⁴⁰Ar/³⁹Ar dating reveal several pulses in formation of the Upper Kolyma gold deposits. The majority of granitoid-related Au deposits and occurrences in the region are related to the oldest (150 Ma) metaluminous granitoid plutons of the subduction nature. ⁴⁰Ar/³⁹Ar dates for Au-quartz mineralization in the Upper Kolyma district correspond mostly to 139–125 Ma, which is a period of less intense igneous and metamorphic activity in the area. We interpret these ages to indicate vein formation by metamorphic fluids, boiling from uplift and decompression, following Early Cretaceous collision-induced metamorphism. Most Sn-quartz, Sn-silicate-sulfide, Sn-polymetallic veins, as well as Ag-polymetallic and U-REE mineralization relates to the ca. 80 Ma plutons, emplaced in an extensional setting.

The ⁴⁰Ar/³⁹Ar data, obtained for Au-quartz vein mineralization, were used as a basis to develop a genetic model that assumes a time interval (from 1 to 15 m.y.) between the ore-mobilizing processes and the timing of ore deposition. Such an interval can be interpreted by virtue of the regional uplift and irregular drop in pressure of fluid systems as the main factors of ore deposition.

Iron- and As-bearing sulfides are typical for all hardrock deposits of the Upper Kolyma district, and they reflect the event and/or remobilization of gold. Pyrite is the main sulfide in greenschist metaturbidities and igneous rocks. Metamorphism of turbidites resulted in pyrite–pyrrhotite transformations with sulfur, arsenic, and metal mobilization. Arsenopyrite assemblages, usually dominating in the ores of all deposit types of the district, are products of geochemical evolution of the above-mentioned mobilized sulfur and arsenic. The Au-quartz vein deposits are characterized by pyrite–arsenopyrite assemblage, and arsenopyrite has almost a stoichiometric composition; the granitoid-related Au- and Sn-quartz veins are characterized by lollingite–arsenopyrite assemblage and As/S > 1 in arsenopyrite; the Sn silicate-sulfide and Sn-polymetallic veins are characterized by pyrite–pyrrhotite–arsenopyrite assemblage and stoichiometric arsenopyrite; the Ag-polymetallic and quartz molybdenite veins are characterized by pyrite–arsenopyrite assemblage and As/S < 1 in arsenopyrite. However, some deposits do not agree with the above-mentioned criteria, which can be explained either by overprinting of several mineralization types in an individual deposit or by metamorphism of its ores. The results demonstrate high importance of re-mobilization of metals due to the later hydrothermal and thermal events.