The age of Ag–Sb deposits of Central Asia and their correlation with other types of ore systems and magmatism

Abstract

Economic Ag–Sb deposits are located within four large ore districts of Central Asia: SE Altai–NW Mongolia, SE Pamir (Tajikistan), Talas (Kyrgyzstan) and Verkhoyansk province (Yakutia), where Ag–Sb ores are spatially associated with tin mineralization. The geology, mineral composition and geochemistry of the Ag–Sb deposits, age of mineralization, distribution and genesis are presented in this paper. Results of new studies show that Ag–Sb ores commonly occur within Sn ore provinces and can be divided into three groups according to their relationships with tin mineralization. Ag–Sb deposits of the first group are spatially isolated from Sn–W ore fields and from metamorphic haloes of Sn-bearing granitoids (pre-granitic deposits of the Mangazeisky ore cluster in Yakutia and deposits of the Asgat-Ozernoe ore zone in the SE Altai–NW Mongolia). A 240 ± 3.5 Ma 39Ar/ 40Ar age of Ag–Sb mineralization was determined for the Asgat deposit (SE Altai–NW Mongolia), which correlates well with the 243 ± 3.7 Ma 39Ar/ 40Ar age of alkaline mafic intrusions (lamprophyre dike). The Ag–Sb ore appears to be younger than Sn–W mineralization (352 ± 6.0 Ma) related with granite of the Yustid complex (355.7 ± 8.6 Ma). The second group comprises granite-hosted Ag–Sb deposits of the Bazardara ore cluster (SE Pamir) of Paleogene age (44 ± 1.5 Ma) located within a tin ore cluster, but separated in time from the Cretaceous Sn mineralization (98.5 ± 1 Ma, Ar–Ar). Ag–Sb ore veins of the third group are located within tin ore clusters and are nearly coeval with tin mineralization (post-granitic Ag rich ore of the Mangazeiskoe, Prognoz and Menkechenskoe deposits, Verkhoyansk province). A close spatial and temporal relationship of Ag–Sb deposits with Sb–Hg mineralization and alkaline mafic magmatism is observed. Helium isotope systematics from the ore-forming fluids of Ag–Sb Akjilga deposit (Pamir) confirm the role of mantle helium in the ore-forming process. Another important indicator of a mantle source in these Ag–Sb deposits is the Hg content in the ores; Hg being a typical element of mantle origin. Isotopic ( 3He/ 4He, 87Sr/ 86Sr, Pb, S) and geochronological data demonstrate that Ag–Sb deposits are polygenetic in sources of ore matter and relate to the mantle-crustal ore-magmatic systems.