Study On Metallogenic Regularity Of Zinc-Copper Ore In Tongkeng Deposit,Dachang, Guangxi

Tongkeng deposit, located in the Danchi metallogenic belt, Northwest Guangxi, is one of the largest world-class deposits in Dachang tin-polymetallic ore-field with the most remarkable metallogenic characteristic. Tongkeng deposit is composed of shallow tin-polymetallic ore body (including large vein-type, thin vein zone type, No.91and No.92) and skarn type zinc-copper ore body in the deep region of the deposit (under355m midsection), in which No.94, No.95, No.96and N0.97are newly discovered. By studying the mineralized alternation, spatial distribution of ore body and its controlling factors, geochemical characteristic of deposit, characteristic of rare earth elements in calcite as well as S isotope, this paper presents the following conclusions:(1) The reason for mineralization and alternation in the deep zinc-copper ore body of Tongkeng deposit is basically found out. The mineralization of zinc-copper ore body is found in Luofu Fm mudstone of middle Devonian System and maristone, which is bedded in general and has the tendency in expansion and shrinkage as well as pinching-out and reproduction; Wall rock alternation occurs to red skarn consisting of garnet and wollastonite, green skarn consisting of chlorite and tremolite as well as actinolite, carbonation, silicification and fluriotization. The green skarn lithification is closely tied with mineralization.(2) The mineralization of zinc-copper ore-body is controlled by bedding gliding fractured zone in the north limb of EW strike Changpo secondary anticline. NE-strike fault is the main ore fluid structure. The bedding fractured zone, SN-strike fold and SN-strike fault are the main host ore structure.The intersection part of NE-strike fault and SN-strike fold are perfect for mineralization enrichment.(3) The zinc-copper ore-body is controlled by hidden phacolite, which occurs in hidden phacolite from NE-strike to NW-strike turning part.(4) It has been shown by the test on microelement that the content of mineral elements in Cu, Zn, Ag, Sb decreases from NE to SW. The zinc-copper ore body becomes further away from the hidden rock mass from No.0ore body to No.96to No.95to No.94. The mineral element in Zn and Cu decreases from4.99%to5.81%to3.40%to3.04%and from0.57%to0.21%to0.27%to0.13%respectively, which indicates that the ore fluid of zinc-copper ore body migrates from NE to SW.(5) The total amount of rare earth elements in calcite of Lame Zinc-copper deposit near to the hidden rock mass ranges from12.85X10"6to43.74X10-6and the LREE/HREE of rare earth elemets ranges from1.15to3.00; while the total amount of rare earth elements in calcite of Tongkeng deposit far away from the hidden rock mass ranges from15.53×10-6to16.17×10-6, the LREE/HREE of rare earth elements ranges from3.22to3.94. Their rare earth elements are similar in characteristic with low quantity and high enrichment in light rare earth elements. The calcite is enriched of light rare earth elements in Tongkeng deep zinc-copper deposit far away from Longxianggai granite. The chemical research on S isotope in the mineral indicates that the534S value of the sphalerite of Lame zinc-copper ore-body ranges from-2.4‰to2.5‰with its average value being0.5‰and the δ34S value of sphalerite of No.96zinc-copper ore-body ranges from-4.3‰to-0.3‰with its average value being-3.6‰.It is indicated that the sulfur isotopic composition is enriched in32S far from Longxianggai granite. As the homology products, the metallogenic material is mainly from Longxianggai hidden granite and the magma fluid results in the mineralization. The decrease in834S value from Lame zinc-copper ore-body to Tongkeng deposit as well as the enrichment in32S is an indication of mixing more material from the stratum.(6) In conclusion, the zinc-copper ore body is found in Longxianggai hidden roof with an elevation ranging within100meters. NE strike fault is the main ore fluid structure for zinc and copper mineralization. The intersection part of NE-strike fault and hidden phacolite are perfect for mineralization enrichment. Based on all these studies, this paper suggests that the Qingcaiyuan area in DaChang ore field is a prospective area for zinc and copper ore exploration.