Relationships Between Gold and Pyrite at the Xincheng Gold Deposit, Jiaodong Peninsula, China: Implications for Gold Source and Deposition in a Brittle Epizonal Environment

Abstract

The Xincheng gold deposit, hosted by the Early Cretaceous 132 to 123 Ma Guojialing-type granitoids in northwest Jiaodong Peninsula, southeast North China craton, formed about 2 billion years later than regional metamorphism of the Archean Jiaodong basement rocks. The Xincheng deposit comprises mineralized zones with three types of hydrothermal pyrite associated with gold, tellurides, and a variety of sulfides: py1 as disseminated euhedral to subhedral grains in altered granitoids around quartz veins; py2 as subhedral grains with brittle cataclastic textures and fractures in quartz-pyrite veins; and py3 as subhedral, partially corroded crystals in sulfide-rich veins or veinlets. All three generations of pyrite are unzoned and have low trace element contents, including very low lattice-bound gold contents: (py1: 0.180 ppm; py2: 0.053 ppm; py3: 0.060 ppm). Given that there is 10 to 15% pyrite in the ore zone at Xincheng, its very low gold content indicates that it contributes <0.2% of gold to the 7.75 g/t gold in the orebody. Instead, over 99% of the gold is present as discrete electrum and/or gold (total range 0.02-59% silver) grains, which are largely sited in fractures at all scales in pyrite, other ore minerals, and quartz. Importantly, visible gold in py3 is also sited on solution-corroded pyrite grains. The pyrite textural and geochemical data indicate that it is impossible to derive the high gold-grade orebodies through local remobilization of originally lattice-bound gold in pyrite. Instead, the gold is interpreted to have been deposited through sulfidation reactions and phase separation of a H2O-CO2 ore fluid during progressive brittle cataclastic deformation associated with seismic activity and regional sinistral transtensional shear movement. This concomitant fluid infiltration and deformation caused episodic deposition and fracturing and corrosion of earlier formed pyrite and deposited visible gold in dilational cracks. The coupled development of the transtensional, rather than normal transpressional setting, and precipitation of gold within dilational veins and wall-rock alteration facilitated the deposition of visible gold and an exceptionally high gold tenor. All deposit characteristics indicate that the Xincheng gold deposit is a member of the epizonal orogenic deposit class.

Regional structural control on the distribution of world‐class gold deposits: An overview from the Giant Jiaodong Gold Province, China

“…(a) Calculated maximum principal stress fields (compression), pre‐130 Ma and pre‐gold mineralization, and (b) minimum principal stress fields for WNW extensional event post‐120 Ma and post‐gold mineralization. Geological map compiled by Lu et al (), L. Q. Yang et al (), and L. Q. Yang, Deng, Wang, Guo, et al (). Palaeostress directions derived from Y. Q. Zhang et al (); Y. Q. Zhang, Li, et al (); T. Zhang and Zhang (); Ren et al (); L. Zhang (); and Charles et al () [Colour figure can be viewed at wileyonlinelibrary.com]…”

“…The Linglong and Taishang gold deposits are situated at the northern segment of the Zhaoping Fault. Modified from L. Q. Yang, Deng, Wang, Guo, et al (). (b) Sketch map of the disseminated/microbreccia‐stockwork orebody and fault zones at the Taishang gold deposit, showing the structural control of the intersection of the Poutouqing Fault and the E–W‐trending faults on gold mineralization and hydrothermal alteration.…”

“…(b) Sketch map of the disseminated/microbreccia‐stockwork orebody and fault zones at the Taishang gold deposit, showing the structural control of the intersection of the Poutouqing Fault and the E–W‐trending faults on gold mineralization and hydrothermal alteration. Modified from L. Q. Yang, Deng, Wang, Guo, et al (). (c, d) Cross‐sections BB’ and CC’ on Lines 15 and 39 [Colour figure can be viewed at wileyonlinelibrary.com]…”

“…Importantly, they show no consistent spatial relationship to granitic intrusions of the same age nor evidence of metal zonation related to thermal gradients surrounding anomalously hot intrusions in cooler host rocks. However, they do show a clear structural control along regional faults (Charles et al, ; Lu et al, ; Song et al, ), and ore and wallrock‐alteration mineralogy, fluid‐inclusion compositions, and stable‐isotope chemistry are similar to more typical orogenic gold deposits, particularly of the epizonal type (Y. M. Qiu et al, ; Fan, Hu, Yang, & Zhai, ; Mao et al, ; Q. Y. Yang, Santosh, et al, ; L. Q. Yang, Deng, Wang, Gou, et al, …”

Geochemistry of Pyrite from the Gangcha Gold Deposit, West Qinling Orogen, China: Implications for Ore Genesis

“…Cook et al (2013) indicated that there may be continuous fluid flux through preexisting pyrite grains, promoting ongoing sulfur liberation and allowing Au precipitation. However, it is unlikely that this process could generate a significant amount of Au (Yang et al, 2016). There should be a mechanism to precipitate the visible Au and further studies should be carried out to determine if the Au in Gangcha gold deposit is present in native form.…”