NOTE Chunzeng Wang á Jinfu Lin á Kaiqiu Dai Geology and structural controls of the Twin Peaks epithermal gold deposit, East Junggar, Xinjiang, China Received: 25 April 2000 / Accepted: 11 January 2001 / Published online: 9 March 2001 Ó Springer-Verlag 2001 Abstract The Twin Peaks epithermal gold deposit, located in East Junggar, China, is hosted by the late Paleozoic Kulankazigan is- land-arc complex. The deposit is structurally controlled by the extensional radial fractures associated with development of the Early Carboniferous Twin Peaks volcanic dome. It is stratigraph- ically restricted to the upper Batamayineishan Formation, which is subdivided into two units: the lower andesite unit that contains the ore bodies, and the upper rhyolite unit. Four hydrothermal alter- ation zones have been identi®ed in both East and West Zones of the deposit. Each zone is characterized by a highly silici®ed core, and then there is an outward progression through adularia±sericite, argillic, and propylitic zones. The presence of adularia and sericite, in addition to the sul®de mineral association, suggests that the gold deposit is of the ``adularia-sericite'' or ``low sul®dation'' type. The East Zone ore body is oset by post-mineralization, high-angle reverse faults that strike parallel to the zone and small-scale, strike- slip faults that strike perpendicular to the zone. Introduction Volcanic-hosted epithermal gold and gold-silver deposits are commonly found around the circum-Paci®c margin, mostly in Mesozoic and Cenozoic volcanic ®elds Hedenquist 1987; White et al. 1995). Exploration for precious metals in northern and north- eastern Xinjiang Uygur Autonomous Region of northwestern China in recent years has been encouraged by the discovery of several epithermal gold and gold±silver occurrences in the Carbo- niferous volcanic ®elds in the accreted Hercynian island-arc com- plexes, such as the well-known Axi gold deposit in the western Tian Shan Mountains Wu et al. 1992; Mu et al. 1996; Wang et al. 1996; Pirajno et al. 1997). In the East Junggar part of the region, several voluminous NW-trending Carboniferous island-arc volcanic ®elds are exposed. A few epithermal gold occurrences, including the Twin Peaks gold deposit, have been recently discovered in these volcanic ®elds. However, few publications exist that describe these new gold occurrences. This paper presents results of our research at the Twin Peaks deposit. We believe that our study of the Twin Peaks deposit will be helpful for a better understanding of gold metallogeny and for guiding future exploration in East Junggar. The Twin Peaks known as Shuangfengshan in Chinese) epi- thermal gold deposit is located in Balikun County, eastern Xinjiang Uygur Autonomous Region. It is geographically in the central part of East Junggar and is north of the eastern North Tian Shan Mountains Fig. 1). It was discovered in 1994 and is one of a series of important gold deposits recently discovered in the vast East Jungger area on the margins of the Gobi desert. Its metal reserve is unknown because the drilling program is still underway, but open- pit mining and heap-leaching started in 1995. An estimate of reserve only in the shallow part of the ore bodies is 8 metric tons of gold. This, however, does not include the metal content of the ``lost ore body'' in the East Zone, which will be discussed later. This paper is intended to introduce the geology and structural controls of this gold deposit. Regional geological setting The Twin Peaks gold deposit is named after the Twin Peaks hill, the highest hill in the study area 1,716.2 m) and visible from a far distance. This hill has two peaks and is located in the center of the study area and north of the ore zones Figs. 2 and 3). It is located in East Junggar, which is underlain by a geologically complex late Paleozoic accreted volcanic island-arc Fig. 1; Wang et al. 1986; Carroll et al. 1990, 1995; Allen and Windley 1993). Termed the Kulankazigan island-arc, it is bordered by the NW-striking Ke- lameili fault zone, which marks the suture of the arc to an earlier accreted arc complex to the south, and the Wulungu fault zone to the north Fig. 1). The Paleozoic sedimentary and volcanic forma- tions in the Kulankazigan island-arc also roughly strike northwest. The oldest formation in the study area is the weakly metamor- phosed Late Silurian sandstone and siltstone Kaokesaiergai For- mation) that crops out about 6 km north of the Twin Peaks deposit Fig. 2). It is surrounded by Early to Middle Devonian clastic and interbedded volcaniclastic rocks, with minor limestones, which are locally intruded by small bodies of Carboniferous andesite and dacite porphyry. All of these rocks were gently folded into NW- to WNW-striking anticlines and then unconformably overlain by vo- luminous Carboniferous volcanic rocks Fig. 2). The Carboniferous eruptive centers and domes are mainly con®ned to the northwest- striking arc system between the two major faults. A NW-trending Jurassic red-bed basin sequence occurs immediately west and southwest of the study area Fig. 2). The Twin Peaks deposit is hosted by rocks of the Batamayi- neishan Formation, which comprises a Carboniferous volcanic ®eld. Andesitic lavas are interstrati®ed with andesitic breccias and Mineralium Deposita 2001) 36: 458±464 DOI 10.1007/s001260100159 Editorial handling: O. Christensen C. Wang &) Earth and Environmental Sciences Program, The Graduate Center of the City University of New York, 365 Fifth Avenue, New York, NY 10016, USA E-mail: wangcz@hotmail.com Fax: +1-718-9973299 J. Lin á K. Dai Department of Geosciences, Guilin Institute of Technology, Guilin, Guangxi 541004, China