Geological characteristics, associated granites and the prospecting potential of the super-large Kaerqiaer-Kumutashi fluorite mineralization belt in the West Altyn-Tagh Orogen, NW China

This paper is the result of mineral exploration engineering.

Objective Significant breakthroughs have recently been made in fluorite prospecting in the western part of the Altyn-Tagh Orogen in NW China. The newly discovered super-large mineralized belt, which includes the Kaerqiaer, Kumutashi, Xiaobaihegou and North Bulake deposits, is an important fluorite resource base. Research on the genesis of fluorite mineralization is lacking. This paper selects typical deposits in the area for research, to reveal the geological characteristics, ore-controlling factors and prospecting potentials of the super-large fluorite mineralization belt in the West Altyn-Tagh Orogen, thus increasing our knowledge of the genesis and improving regional prospecting for the mineralization.

Methods Based on detailed field investigation, this paper uses LA-ICP-MS zircon dating, geochemistry and Hf isotope analysis to define: (1) The age of rock formation and mineralization; (2) The genesis of ore-controlling alkali-feldspar granite and fluorite mineralization; (3) Summarises the ore-controlling elements and prospecting characteristics of the area; (4) Conducts mineralisation prediction through geological, geochemical and remote sensing data; (5) Analyses the prospectivity of the region.

Results The fluorite mineralization is of hydrothermal origin closely related to alkali feldspar granites, and is controlled largely by NE-trending faults and, to a lesser extent, NEE- and E-trending faults. The host rocks are plagioclase gneiss and carbonate rocks in Altyn Group. The main types of ore include massive, vein and breccia containing early white and later purple fluorite, calcite and minor amounts of quartz, apatite and tainiolite. The alkali feldspar granite at the Kumutashi fluorite deposit has a zircon U-Pb age of (450.0 ± 2.7) Ma, ε_Hf(t) values ranges from -5.33 to +6.45, and TDM2 age between 1767 Ma and 1020 Ma. The geochemical data also shows that the alkali feldspar granite is potassic, metaluminous, high differentiated and genetically related with F-rich rocks. The granite is enriched in Rb, Th, U, La, Ce, Nd, Zr and Hf, depleted in Ta, Nb, Sr, P, and Ti, and has a high ΣREE content. These characteristics are indicative of A-type granites emplaced during the Late Ordovician and derived from a mixed crustal and mantle magma during post-orogenic extension.

Conclusions The widely distributed alkali feldspar granite with high F and ΣREE contents have high prospectivity for fluorite, tin, rare metals, and REE. Thus, the combination of alkali granites, NE-trending faults, and carbonates in the Altyn Group are consisted prospective for large fluorite deposits.