Age and genesis of the Dadonggou gold deposit in the Liaodong mining district: Evidences from geology, chronology, geochemistry and isotope

The Dadonggou gold deposit is located in the Liaodong Mining District (LMD) at the northeastern margin of the North China Craton (NCC). Orebodies of the deposit are mainly hosted in the sericite phyllite of the Gaixian Formation of the Paleoproterozoic Liaohe Group, and they are are spatially related to the Mesozoic quartz diorite. In this paper, a combined study of deposit geology, pyrite Re-Os and zircon U-Pb dating, geochemical and Hf isotopic analyses upon ore-related intrusion, together with sulfur isotope of the sulfides was conducted to constrain the geological setting and ore genesis of the Dadonggou deposit. A paragenetic sequence with three periods has been identified as syngenetic/diagenetic pyrite (I), metamorphosed pyrite-arsenopyrite (II) and hydrothermal (III) periods, among which the third period can be further subdivided into pyrite-arsenopyrite (III1), polymetallic sulfide quartz (III2) and pyrite-bearing quartz-carbonate (III3) stages. Pyrites from stage III yielded Re-Os isochron age of 130 +/- 18Ma (n=5, Initial Os-187/Os-188=1.60 +/- 0.42), which is consistent with the emplacement age of ore-related quartz diorite (133 +/- 1Ma), indicating that Au-mineralization occurred in the Early Cretaceous. Sulfides from ore-stages III1-2 have delta S-34 values ranging from 3.0 parts per thousand to 4.8 parts per thousand, which are distinct from those of sedimentary pyrite from the first period (8.9 parts per thousand similar to 10.2 parts per thousand) and sedimentary-metamorphic rocks from the Paleoproterozoic Liaohe Group (7 parts per thousand similar to 23 parts per thousand), suggesting that the S element was derived from a magmatic source. The ore-related quartz diorite is characterized by enrichment in large ion lithophile elements (i.e., Rb, Ba and U), and moderately depleted in high field strength elements (i.e., Nb and Ta) with low epsilon(Hf)(t) values (-6.38 similar to-2.82). Combined with geological data of synchronic intrusions in the district, the source of the pluton was likely derived from a magma mixing between the mantle-derived mafic and the crust-derived felsic magmas. Combining available data results in the district, we propose that the Dadonggou is a type of mesothermal gold deposit, and it is genetically related to a synchronic oxidized diorite magma formed in the peak period of destruction of the NCC during the Early Cretaceous