Geological-geochemical Features Of The Pinglidian Gold Deposit, Jiaodong Peninsula, China

The Pinglidian quartz-vein gold deposit is located within the Pinglidian and Zhuyoudian town of northwestern Laizhou city, and hosted in the Precambrian metamorphic basement. The outcropped Archean basement strata belong to the Qishan Formation of Jiaodong Group consisting of biotite plagioclase genesis and biotite monzonite genesis. The gold-bearing quartz vein was controlled by eleven concealed NE-NNE-trending faults(i.e. F1 and F4) known as the secondary faults of Jiaojia fault. The main orebody in the Pinglingdian gold deposit was the No.1 gold-bearing quartz vein. Narrow and symmetrical alteration zone developed along the two sides of quartz vein. It turns out to be quartz vein, sericitic biotite plagioclase genesis, lightly potassium-altered biotite plagioclase genesis and fresh biotite plagioclase genesis from the orebody to wall-rock in the alteration zone. The types of ores are mainly quartz-vein type with minor pyrite-sericite alteration type and gold-bearing sericitic alteration type.Ore minerals are mainly pyrite, electrum and native gold, with subsequent chalcopyrite, galena and sphalerite. Gangue minerals are mostly quartz, biotite, sericite and K-feldspar. Occurrence of native gold in the ore is crystal interface-gold, crack-gold and secondly inclusion gold. The main ore textures include grain structure, interstitial texture, cataclastic texture, poikilitic texture, emulsion texture, metasomatic texture. The ore structures are mainly disseminated and veinlet structure. Wall-rock alteration including sericitization, pyrite-sericite-quartz alteration, silicification, potassic alteration, chloritization and carbonatization, have been strongly developed in the district. The silicification and pyrite-sericite-quartz alteration have closest relationship with gold mineralization.Gold mineralization in Pinglidian gold deposit can be divided into hydrothermal mineralization period and supergene oxidation period. The hydrothermal mineralization is further divided into four stages: quartz-pyrite stage(I), gold-quartz-pyrite stage(II), gold-quartz-polymetallic sulfide stage(III), quartz carbonate stage(IV). II, III stage is the main stage of gold mineralization.Fluid inclusion study in the Pinglidian gold deposit shows that the ore-forming fluid is characterized by low salinity(7.72-13.50 % Na Cl eqv) and low density(0.801-0.977g/cm3), with ore-forming temperatures of 170-310 °C. D-O isotopic compositions reveal that the ore-forming fluids are mainly metamorphic water, with the input of minor meteoric water. Study on sulfur isotopes of ore minerals show that the ore-forming materials are mainly originated from Jiaodong group. In conclusion, the Pinglidian gold deposit is classified as an orogenic gold deposit.