| The Zhongtiao Mountain ore-concentration area is one of the most important copperdeposits in China, which is composed of series of large-and medium-sized copperdeposits, such as the superlarge Tongkuangyu copper deposit, the medium-sizedHujiayu-Bizigou copper deposit and the medium-sized Luojiahe copper deposit. Thecomplicated geographical condition in the ore-concentration is an important metallogenicfactor. The “Hu-Bi Type” copper deposit, represented by the Hujiayu copper deposit andthe Bizigou copper deposit, is one of the most essential mineral deposits in the study area.The Hujiayu copper deposit includes but is not limited to the Nanhegou deposit andthe Tongmugou deposit. The copper orebodies, hosted in the Bizigou Formation which iscomposed of siliceous albitite, impure marble and black schist, are mainly instratiform-like shape and partially in lenticular shape which are controlled byfolds and fault fractures. Its mineralization type is characterized by vein-like, lumpy andimpregnated, the major ore minerals are chalcopyrite and other metallic minerals likepyrite, molybdenite, etc. Its minerals are in metasomatic, milk-solouble andcrystalline-granular texture and in impregnated, vein-like, lumpy and brecciaous structure.The results of analysis of metallogenic element show that Cu, Au and Ag are closelyrelated (the correlation coefficient is greater than0.75) and can be regarded as the directindicator elements.The host rocks show a negative anomaly of Nb, Ta and Ti which is similar to those ofmagma in the subduction zone. Amphibolite, biotite quartz schist and siliceous albititeshow an obvious enrichment in LREE and the pattern characterized by an obviousrightward shift of all curves. The total rare elements of impure marble and siliceousalbitite varies within a wide range, sharing the similar characteristics of REE in modernhydrothermal sedimentary deposits, which is regarded as the result of different reactiondegree between sea water and rocks and varied mixability between hydrotherm and seawater.In terms of the composition of sulfur isotope, the “Hu-Bi Type” copper deposit ischaracterized by homogeneous and mixed sulfur isotopes, which shows multiple origins ofits sulfur, partly from deep-seated basic magma and other from carbonate in sea water, and is different from endogenous mineral deposit or sedimentary deposits. Moreover, thecharacteristics of sulfur isotopes of veinlike orebodies differ significantly from those ofveinlet-impregnated orebodies in the deposit.In veinlike orebodies, heavy sulfur decreases drastically and light sulfur increases tosome extent, which shows that on one hand, influenced by extrusion and shearing action,light sulfur moves easily towards structural fissure in metamorphic process, and on theother hand, the late mineralization derives from the early.Compared to the typical exhalative sedimentary deposits, the Nanhegou deposit inthe Hujiayu and the Tongmugou deposit indicate that high consistency of the geologiccharacteristics between the Hujiayu copper deposit and thetypical exhalative sedimentary deposits. In addition, a series of contrast on thegeochemical characteristics of host rocks in the deposit, modern red sea basin hot brinechemical sediments and domestic typical exhalative sedimentary deposits also show highconsistency. It’s thus believed that ore-controlling rocks in Hujiayu Deposit belong toexhalative rocks formed by hydrothermal sedimentation and the genetic type of themineral deposits belongs to the exhalative sedimentary deposits.After the analysis of the tectonic setting and evolution of the Zhongtiao Rift andstudy of the geological setting of mineralization of the “Hu-Bi Type” copper deposit, thethesis holds that the tectonic setting of the Hujiayu copper depositwas back-arc basin formed after subduction through two-stage mineralization. The earlystage, around2060Ma, is the metallogenic period of the main part of the deposit. The latestage of metamorphism and deformation influenced by the Zhongtiao Movement,especially the Zhongtiao Movement Act I. The late period of mineralization enlargesoriginal orebodies of the deposit and enriches its grade, coming out “Saddle-shaped”orebodies in the hinge zone of fold, which did not change basic characteristics of theoriginal deposit. |
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