Timing and origin of orogenic gold mineralization in the Kanggurtag area, NW China

The Kanggur, Kangxi and Matoutan deposits are three important orogenic gold deposits located in the Kang-gurtag gold mineralization belt of Eastern Tianshan, NW China. These deposits are hosted in low-grade metamorphic (greenschist-facies) volcaniclastic rocks of the Early Carboniferous Yamansu Formation. The orebodies are distributed in approximately E-W-striking shear zones and show evidence of hydrothermal alteration and four deformation events. The first deformation (D1) is associated with progressive regional N-S shortening without growth of gold mineralization. The second deformation (D2) is manifested by right-lateral shear zones under ductile conditions, which triggered the initial enrichment of gold in the stage I pyrite. The third deformation (D3) is characterized by a transpressional event under ductile-brittle conditions and formed stage II-IV pyrites with dominant Au mineralization; the native gold is mainly distributed in the interstices or interface of the pyrites. The fourth deformation (D4) is archived by post-collision extensional structures accompanied by magma emplacement and numerous limonite and comb-like quartz veins. Six pyrite samples (stage III) separated from the Kanggur deposit yield a Re-Os isochron age of 321 +/- 6.7 Ma (MSWD = 3.0, initial Os-187/Os-188 = 0.35 +/- 0.22). Three pyrite samples (stage III) separated from the Kangxi deposit yield a Re-Os isochron age of 327 +/- 4.5 Ma (MSWD = 1.2, initial Os-187/Os-188 = 0.94 +/- 0.12). The delta S-34 value significantly increases from stage I pyrite (-37.3 parts per thousand to -25.5 parts per thousand, average = -32.2 parts per thousand) to stage II-IV pyrite (-0.90 parts per thousand to 6.30 parts per thousand, average =1.96 parts per thousand), indicating that sulfur in stage I pyrite migrated from sedimentary sources whereas in stage II-IV pyrites it was derived from the pyroclastic rocks in the country rocks. The H-O isotopic compositions of quartz show that the fluid in stage I (delta O-18(w) = 2.25 parts per thousand to 5.15 parts per thousand, delta D-2 = -66.0 parts per thousand to -42.5 parts per thousand) was metamorphic water and the fluid in stage V was mixed with a large proportion of meteoric water. The fluids in stages II-IV maybe a second hand magmatic origin related to the andesite in the country rocks. Therefore, we propose that Au mineralization in the Kanggur, Kangxi and Matoutan deposits derived mainly from a metamorphic fluid source associated with the pyroclastic rocks in the country rocks. In addition, we conclude that these deposits are orogenic gold deposits that formed during the Late Carboniferous collisional tectonism (ca. 320 Ma) and the epithermal Au deposits (ca. 280 Ma) maybe associated with the post-collision extensional setting.

Automated summary

The Kanggur, Kangxi, and Matoutan deposits are important orogenic gold deposits located in the Kang-gurtag gold mineralization belt of Eastern Tianshan in Northwest China. These deposits formed during the Late Carboniferous collisional tectonism and are associated with metamorphic fluids and pyroclastic rocks in the country rocks. The deposits experienced four deformation events and show evidence of hydrothermal alteration.