Middle-low temperature hydrothermal copper deposit.

There is an ancient mine in the deposit area. The Nulasai deposit is the earliest Cu mine in Xinjiang, NW China, and has been mined and smelted since the warring state period and shows the highest Cu grade (averaging 1.34%) in the district. The richest Cu ores (3.27%) occur in the center part of the deposit, and ore minerals include predominantly bornite, chalcocite, and chalcopyrite.

Nulasai deposit region is mainly covered by Permian volcano-sedimentary succession, including the Lower Permian Wulang Formation (P1w), the Middle Permian Xiaoshansayi Formation (P2x), and the Quaternary sediments. The faults mainly cut the Middle Permian Xiaoshansayi Formation and granite porphyry, and associated fracture zones and breccias are well-developed. The tectonic fracture zones are about 10–30 cm in width and consists primarily of granite porphyry fragments and rock powders; the fault breccias are angular and partially cemented by late calcite veins. Distribution of orebodies are controlled by fault structure zone between the two major faults.

Two main ore zones were identified by geological surveying: the south and the north. There is one recognized Cu orebody in the south ore zone. Three defined Cu orebodies in the north ore zone. These orebodies are situated subparallel to the F1 and F2 fault, which trend northwest. The No. Ⅰ, Ⅱ, Ⅲ Cu orebodies in the north ore zone are coexistence with Pb and Zn mineralization, and the No. Ⅳ orebody in the south ore zone coexistence with Ag orebodies. Cu orebodies are mostly found in granitic porphyry and tuffaceous sandstone as veins and lenticular bodies. As a typical example, the No. Ⅱ-1 orebody looks to be vein type, and compose of calcite-barite-bornite-chalcocite-chalcopyrite veins, and Calcite-barite-sphalerite-galena-chalcopyrite veins. The orebody is inclined downwards (60°–82° S), extends up to 500 m, and the thickest part reaches 12 m, with an overall east–west distribution. Average ore grades are 2.3 % Cu, with additional Pb (3.65 %) and Zn (7.96 %) mineralization.
The stage I is concentrically distributed in the quartz diorite porphyry, comprising mainly of magnetite–quartz–chalcopyrite ± bornite ± K-feldspar ± plagioclase veins, and is associated with local potassic alteration. The stage II represents the main hydrothermal stage at the Nulasai, and is mainly developed in the shallow depths compared to stage I. The stage III is characterized by the presence of significant copper and minor lead and zinc mineralization.

The Nulasai deposit is located in the northern margin of the western Awulale Cu district with copper ores of more than 2 Mt (average grade: 1.34%). The Permian Wulang Formation, the Xiaoshansayi Formation, and the Quaternary sediments comprise the Permian volcano-sedimentary succession that mostly covers the Nulasai deposit area. The thick basalt, tuffaceous sandstone, and basaltic andesite comprise the Wulang Formation, which is mostly exposed in the northern portion of the deposit. Of these, the Rb-Sr isotopic age of the basalt is 298 ± 7 Ma. The Xiaoshansayi Formation consists mostly of conglomerates and sandstones that are angularly unconformable and are extensively exposed in deposits overlying the Wulang Formation, which formed earlier than 281.6 ± 1 Ma. Quaternary sediments are alluvial sand, coarse gravel, and debris, mainly distributed on the west side of the mining.

Other Regions, Features and Areas containing this locality

References