Ore-forming age and tectonic setting of the Linjiasandaogou gold deposit in the Liaodong Peninsula,northeast China:constraints from geochronology and geochemistry

The Linjiasandaogou gold deposit is located in the Qingchengzi Orefield,North China Craton,China,and has not attracted many studies.We present geochronological,whole-rock geochemical,and Sr–Nd–Hf isotopic data to constrain the age and tectonic setting of the mineralization.U–Pb dating of zircon from pre-and post-ore dikes indicates the Linjiasandaogou Au deposit formed at ca.227–226 Ma.The granite porphyry(ca.227 Ma)and quartz diorite porphyry(ca.228 Ma),which are slightly older than the mineralization,have(;Sr/;Sr)i-=0.7127–0.7162,εNd(t)=–13.7 to–17.0,andεHf(t)=–14.6 to–16.9,and display enrichment in light rare earth elements and large ion lithophile elements and depletion in high field strength elements.Two lamprophyres(226 and225 Ma),which are slightly younger than the mineralization,have higher(;Sr/;Sr)i(0.7165–0.7216),negativeεNd(t)(–11.2 to–14.3)andεHf(t)(–15.6 to–18.6)values,and are enriched in light rare earth elements but depleted in high field strength elements(Nb and Ta).The geochemical characteristics of the granitoid and lamprophyres indicate a lower crustal and enriched mantle source,respectively.We infer that the Linjiasandaogou Au deposit formed in a postcollisional tectonic setting,following the collision between the North China,Yangtze craton,and Central Asian Orogeny in Triassic.

Source of Ore-Forming Fluid and Material in the Baiyun Gold Deposit, Liaoning Province, NE China: Constraints from H-O-S-Pb Isotopes and in-situ Analyses of Au-Bearing Pyrites

The Baiyun deposit is a large gold deposit at the western end of the Liaoji rift zone in Liaoning Province, which has produced both auriferous quartz-vein type and altered-rock type mineralization. The ore bodies are mainly hosted in schist from the Gaixian Formation of the Liaohe Group. A detailed field geological survey showed that the quartz-vein type gold ore bodies are distributed in the near EW-trending and occur in the extensional tectonic space of schist in the Gaixian Formation, and the altered-rock type gold ore bodies are distributed in the near EW-trending structural belt and occur near in the Gaixian Formation of biotite schist, biotite granulite, marble and the upper footwall of dike. To further elucidate the source of ore-forming fluid and material in the Baiyun gold deposit, the H-O isotopes for quartz, S and Pb isotopes, in-situ trace elements for sulfides from quartz-vein and altered-rock type mineralization were studied. The H-O isotopic δD_(V-SMOW) and δ^(18)O_(H2O) values of the auriferous quartz range were from-88.8‰ to-82.2‰ and-1.95‰ to 4.85‰, respectively, suggests that the ore-forming fluids were mainly magmatic water with minor meteoric water. The distribution ranges of in-situ S isotopic compositions of Au-bearing pyrite in the quartz-vein type and altered-rock type ores were-8.38‰–-10.47‰(with average values of-7.89‰) and 11.38‰– 17.52‰(with average values of 11.55‰), respectively, indicating that the S isotopic compositions of the two ore types were clearly different. The in-situ Pb isotopic ratios changed almost uniformly, which showed that they had the same lead isotopic source. Based on the analysis of S and Pb isotopic compositions, the metallogenic materials in the Baiyun gold deposit were primarily from deep magma, and some wall rock materials may have been mixed in the metallogenic process. Co/Ni diagram shows that most Au-bearing pyrites have magmatic-hydrothermal or sedimentary alteration properties, and Au/As ratios were between 0.001 and 0.828(the average value was 0.07), indicating that the ore-forming fluid in the Baiyun gold deposit may have been deep magma. Combining the geological, trace element, and isotopic data, as well as data from previous studies, we propose that the Baiyun gold deposit is a magmatic-hydrothermal ore deposit.