Details

Autor(en) / Beteiligte

• Pavlova, G. G.
• Borovikov, A. A.

Titel

Silver-antimony deposits of Central Asia: physico-chemical model of formation and sources of mineralisation

Ist Teil von

• Australian journal of earth sciences, 2010-01, Vol.57 (6), p.755-775

Ort / Verlag

Taylor & Francis

Erscheinungsjahr

2010

Quelle

Taylor & Francis

Beschreibungen/Notizen

• Questions on the origin of Ag-Sb deposits are considered for several large economic ore districts in Central Asia: southeast Pamir (Tajikistan), Talas in northern Tien Shan (Kyrgyzstan), southeast Altai and northwest Mongolia, and Verkhoyansk province (Yakutia). The Ag-Sb mineralisation of Central Asia is spatially and temporally associated with alkaline mafic magmatism, and occasionally with coeval granitoid magmatism. Ag-Sb deposits have close spatial and temporal relationships with granitoid and alkaline mafic magmatism. The Ag-Sb deposits were formed in the temperature range 50-280°C, from Ag-specific reduced two-phase hydrothermal fluids containing a highly concentrated chloride solution (NaCl > FeCl 2 > CaCl 2 > KCl > MnCl 2 ) and a high-density CO 2 + CH 4  ± N 2 gaseous phase. Fluid salinities range widely from 40 to 0.1 wt% NaCl equiv. Geochemical specialisation of Ag-Sb ore is caused by chemical features of chloride brines enriched in Ag, Sb, Pb and Cu, with a relatively low Au content (≤10 −6 mol/kg) within a pH of 3.5-4. The highest temperatures, concentrations of solutions and ore elements in the ore fluids were found in early quartz of siderite-tetrahedrite veins from below-ore level of the ore-forming system. Vertical zonation of the Ag-Sb mineralisation is caused by precipitation of different mineral associations from the same solution with temperatures decreasing towards the upper parts of the system. Sufficient vertical range of mineralisation (600-800 m) and relatively low Ag contents in the ore (300-600 ppm) result from the temperature decrease and absence of geochemical barriers. Higher temperature gradient and dilution of magmatogenic fluid with meteoric water was a geochemical barrier for the Ag-rich ore formation in a narrow (about 400 m) main ore deposition zone. Lateral zonation of Ag-Sb mineralisation is related to a staged development of the ore-forming process and deposition of different stage mineral associations at the beginning and end of the hydrothermal process. The Ag-Sb deposits are polygenic in terms of sources of ore elements and ore-forming fluids. Ore elements may have been inherited from magmatic and terrigenous host-rocks of different ages. Temporal correlation of the Ag-Sb mineralisation with alkaline mafic magmatism, He isotope composition and Hg contents in the ores confirm participation of a mantle source in the formation of the Ag-Sb deposits.