Ore-Clastic Olistostromes, Ore Clasts, and Allochthonous Antimony–Mercury Deposits in the Alay Range, Southern Tien Shan

Based on the detailed study of outcrops, two generations of ore clasts were recognized in clastic haloes around allochthonous antimony–mercury deposits: (1) early generation composed of in situ fragments of older autochthonous deposits (ore clasts) and (2) late generation of fragments related to the destruction of ore-bearing allochthons and found as exotic inclusions in flysch and olistostromes. Ore clasts reside in the terrigenous (pre-flysch) sequence that makes up the upper part of terrigenous–carbonate nappes and olistoplaques in the lower flysch–olistostrome sequence. Thus, they belong to allochthonous units. The terrigenous sequence differs from the younger flysch sediments by a relatively small thickness, predominantly clayey composition, and absence of rhythmic bedding and large erratic blocks. It is also characterized by the synsedimentary volcanic activity with the eruption of intermediate and acid igneous rocks, silicification, and ore mineralization in the lower part of the sequence, the maximal mineralization being confined to the boundary with underlying limestones. Relative to the terrigenous sequence the flysch–olistostrome sequence, which hosts ore-bearing allochthons, is distinguished by the primary attitude, greater abundance of ore clasts, and higher extent of ore disintegration. Some genetic features of autochthonous and allochtonous jasperoid deposits are considered. Their differences in age, host environment, formation depth, vertical extent of ore deposition, and zoning are also outlined.