Gold remobilization of the Sanshandao gold deposit, Jiaodong Peninsula, Eastern China: Perspective from in-situ sulfide trace elements and sulfur isotopes

Abstract

The Sanshandao is a typical altered-rock-style gold deposit (>260 t @ 3.96 g/t). The deposit is located at the northernmost end of the NE-trending Sanshandao fault in the northwestern Jiaodong Peninsula. The orebodies are mainly hosted by the footwall (minor in hanging-wall) of the fault, which cut Jurassic granites. According to the mineral assemblage and crosscutting relationship, five hydrothermal/mineralization stages were identified: (I) veinlet-disseminated quartz + pyrite ± chalcopyrite, (II) quartz + pyrite + chalcopyrite + native Au veining, (III) quartz + pyrite + galena + sphalerite + native Au + chalcopyrite veining, (IV-a) veinlet-disseminated siderite + pyrite + galena + sphalerite, (IV-b) ore-barren siderite, and (V) ore-barren calcite veining. Stages II and III auriferous pyrite contains visible native gold, and can be divided into four generations (Py2a, Py2b, Py3a, and Py3b). Py2a contains little native gold, whereas Py2b, Py3a, and Py3b contain much coarse-grained native gold. Gold in these pyrite generations correlates positively with the As content. Typical Py2a and Py3a porous/sieve-like texture indicates that Au remobilization has occurred, which may have controlled mainly by coupled dissolution-reprecipitation (CDR). Relative Sb-Te enrichments in Py2b and Py3a imply that a melt with low-melting point chalcophile elements (LMCEs) also facilitated Au remobilization by efficiently scavenging Au from preexisting minerals. Combined with the trace element compositions, we show that CDR may have liberated Au and LMCEs, and the subsequent fluid and LMCEs melt have altogether caused Au remobilization. The narrow δ34SV-CDT range of the pyrite from stages II-III (11.75–12.22‰ (Py2a), 10.83–12.39‰ (Py2b), 11.63–12.88‰ (Py3a), 11.91–12.67‰ (Py3b)), together with the compiled S-isotope dataset (from literature data) (δ34SV-CDT = mostly 7–10‰), indicate that reduction of marine sulfates represents the main sulfur source.