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Home , Arsenopyrite

0393-000066 The forming conditions of Alyaskitovoe tin-tungsten deposit, Russia

Corresponding author: Elena Anikina, IGEM RAS, [email protected]

Co-authors: Gennady Gamyanin, IGEM RAS, [email protected]

The Alyaskitovoe Sn-W deposit is located at the boundary between the Kular-Nersko terrane and the Verkhoyansk fold-thrust belt. It is localized in the tin-tungsten sublatitudinal metallogenic zone. The deposit area is composed of Upper Triassic sandstone-shale intruded by granite porphyry stock (98 MA Rb-Sr). Stock refers to the formation of young Li-F granites (P2O5 = 0.22- 0.56%, F = 0.12-0.21%, Sr = 9224-688g/t, Li = 47-252g/t, Rb = 61-194g/t). Stock and enclosing hornfels dissected by series of steeply dipping quartz veins meridional strike (L = up to 700 m, M = 0.4-0.6 m). Veins are accompanied by wallrock changes. It is greisenization in granitoids (up to 3 m) and tourmalinization – in hornfels (0.5 m).

Several paragenetic associations are identified. Metasomatic: molybdenite-apatite1-tourmaline1- quartz-muscovite, tourmaline2-apatite2-fluorite-arsenopyrite-hydromica. Ore: - -tourmaline-arsenopyrite-quartz, pyrrhotite--sphalerite-, molybdenite- matildite-aramayoite-galena-(Bi-) Sb-gustovite, hubnerite-Ag-sulfoantimonite-calcite- quartz.

Fluid inclusions (FI) in quartz of greisen and ore veins were studied. Temperature of homogenization of greisen inclusions is 460-480°C. FI contain weakly concentrated solutions (4.9- 3.3 wt.% NaCl-equiv), the gas phase is presented СО2 (29.6-78,2 mol.%), СН4 (11.1-21.8 mol.%). FI in quartz of ore veins contain a liquid phase with concentration 9.2-3.3 wt.% NaCl-equiv and homogenization temperatures of 290-380°С. In a gas phase of FI contains СО2 (53.1-97.4 mol.%), СН4 (2.6-11.2 mol.%). Homogenization of FI in late quartz is 180 to 150°С, the concentration is 4.9 3.3% wt.% NaCl-equiv with predominance CaCl2 and KCl (Teut -51¸-49°С). Gas phase contains СО2 (0-93.0 mol.%), СН4 (7.0-20.4 mol.%).

The isotope composition of and sulfosalts were analyzed. δ34S values vary from - 3.0 to -5.6‰ in arsenopyrite, from -4.1 to -5.7‰ in pyrite and molybdenite, from -7.5 to -9.1‰ in sulfosalts. In general, to note small variations and shift towards negative sizes of values δ34S has been noted.

The analysis of oxygen isotope composition of quartz has shown some increase in values δ18O from quartz of granits (+13.4‰) to vein quartz (+14.1 to +16.3 ‰). At studying of large crystals of quartz (1-8 cm) the tendency of increase in values δ18O from the basis (+13.6 ‰) to a head (+18.0 ‰) has been noted. At the temperatures estimated by results of studying of fluid inclusions, water of a fluid equilibrium with vein quartz will change from +6.0 to +11.3 ‰ that corresponds to water of a magmatic origin. With the big share of confidence it is possible to assume the contribution of meteoric waters at last stages of deposit formation.

At the heart of formation model is a genetic link Alaskitovoe deposit with young (100±5 Ma) lithium fluoride magmatism. Crystallization of massif completed at 600-650°C. Mineralization is formed at shallow levels (~1 km) from gas saturated fluid, the source of which are deeper levels of the magma chamber. Further formation occurs at decrease in temperature to 150°C, and changes of fluid composition from the highly mineralized bicarbonate-calcium-potassium at formation of Li-F granites and greisen to moderately mineralized bicarbonate-calcium-potassium-sodic at formation of productive associations. СО2 concentration in the gas phase increases. Isotopic data suggest the source of magmatic origin with participation of meteoric waters during mineralization.