Multi-isotopic And REE Geochemistry On Tracing Formation Of The Dajiangping And Dabaoshan Sulfide Ore Deposits In Guangdong Province, South China

Super-large scale metallogenic belt was developed in Guangdong province between the ancient Yangtze and Cathaysia cratons, Southeast China. Two reprensentative deposits including the Dajiangping pyrite deposit and dabaoshan polymetallic sulfide deposit are selected in this study. As there are much controversy and uncertainties for mineral genesis till now. Based on the comprehensive geological setting, detailed studies on the systematic geochemistry including applied new mineral geochemical method for ore genesis have been carried in this study. Conbined with geological background, their ore deposit genisis are discussed. These explorations provide a important reference for regional metallogenic information as well as the theory studies on geochemical sulfide deposits.Molybdenum isotope was explored as a the new tracer for the low-medium temperature hydrothermal ore-forming systems. The results from twelve hydrothermal syndepositional sillcalite and chert samples from the Dajiangping pyrite deposit show that theδ97/95Mo values of the OrebodyⅢrange from -0.02‰to 0.29‰, with a narrow range, In contrast, the values of the OrebodyⅣdisplay a larger variation, especially, the five samples from the main ore bed all show strong negative values. The OrebodyⅢlikely deposited from submarine exhalative hydrothermal fluids under a relatively strong reducing environment and the OrebodyⅣmay have also been influenced by hydrothermal superimposition in a more oxidized disequilibrium condition. In addition, theδ97/95Mo values of the OrebodyⅣare clearly negative, together with the values increasing stratigraphically upward in the ore beds, suggesting that the metallogenic environment of the OrebodyⅣis different from the open oceanic systems. There might be dynamic fractionation in this restricted environment. The molybdenum isotope can be used as an effective tracer for the ore-forming fluid and metallogenic environment.Geochemistry characteristics from other isotopes such He,Ar,Pb and S also illustrated that the metallogenic materials and ore-forming fluids are different between the OrebodyⅢand OrebodyⅣ. There are similar pb and S isotope compositions between the sulfide and wall rock (206Pb/204Pb,207Pb/204Pb,208Pb/204Pb are 18.266,15.641,38.558 VS 18.244,15.712,38.647, respectively;δ34S was -19.4%o VS-18.5‰), as well as the average of 3He/4He is 1.48×10-6 and its R/Ra of 1.04, which indicates that the metallic ore-forming materials mainly derived from clastic formation and the ore-forming fluids might be atmospheric saturation water (seawater) in the OrebodyⅢ. However, the pb and S isotope compositions from Orebody IV show that the metallic ore-forming materials were from baseal statra and sulfur mainly derived from seawater sulfate. In addition, the average R/Ra of 2.42 indicates that the mantle ore-forming fluids might be involved. The sulfides with obvious positive Eu abonormal also infer that there has been experienced high-temperature hydrothermal superimposed during the orebody IV mineralization.Considering there are different bedding or formset in the sulfide ore, a comparative method between the massive orebody and vein orebody was introduced in the studies on the dabaoshan polymetallic deposit. The He-Ar isotope compositions between massive orebody and vein orebody was different. the average R/Ra of the massive orebody was 3.01 and its ore-forming fluids mixed with mantle fluids and atmospheric saturation water (seawater), in contrast, the ore-forming fluids of the vein orebody show the crust materials added characteristics with R/Ra of 0.6. The Pb and S isotope compositions in massive orebody and vein orebody was relative homogeneous that theδ34S values of most sulfide was zero balancing and the pb isotope compositions (the average values of 206Pb/204Pb,207Pb/204Pb,208Pb/204Pb was 18.946,15.735,38.990, respectively) mainly falled the field between the upper crust and fold belt, which suggested that both of their ore-forming materials were mainly from earth deep-seated. However, the REE distribution pattern of these two orebody was apparent different. The massive orebody has typical positive Eu abnormal and enriched LREE, showing the hydrothermal exhalative sedimentary characteristics. Meanwhile, The REE distribution pattern from vein orebody mainly displaying the similar specificities with Granodiorite porphyry that infer the ore-forming fluids of vein orebody might be related with the granitic magmatic fluids, besides some vein orebodies also may be from epimagma derived from the activated massive orebody transfer. There were indeed generated two mineralization in Dabaoshan Polymetallic deposit, One period was associated with volcanism hydrothermal mineralization in Devonian and the other was superposed magmatic mineralization during the stage of Yanshan.Based on fine systematical studies and comprehensive comparative analysis between the Dajiangping pyrite deposit and the Dabaoshan polymetallic sulfide deposit, both of them show hydrothermal sedimentary and superimposed mineralization characteristics. The former is SEDEX-type deposit associated with the hot water, the latter is VMS-type deposit associated with the volcanogenic mineralization. Structural setting, ore formation and contemporaneous fault with the magma emplacement should be as the main exploration point.