Application of tensor CSAMT with high-power orthogonal signal sources in Jiama porphyry copper deposit,South Tibet

The Jiama porphyry copper deposit in Tibet is one of the proven supergiant copper deposits in the Qinghai-Tibet Plateau at present,with the reserves of geological resources equivalent to nearly 20×10^(6) t.However,it features wavy and steep terrain,leading to extremely difficult field operation and heavy interference.This study attempts to determine the effects of the tensor controlled-source audiomagnetotellurics(CSAMT)with high-power orthogonal signal sources(also referred to as the high-power tensor CSAMT)when it is applied to the deep geophysical exploration in plateaus with complex terrain and mining areas with strong interference.The test results show that the high current provided by the highpower tensor CSAMT not only greatly improved the signal-to-noise ratio but also guaranteed that effective signals were received in the case of a long transmitter-receiver distance.Meanwhile,the tensor data better described the anisotropy of deep geologic bodies.In addition,the tests also show that when the transmitting current reaches 60 A,it is still guaranteed that strong enough signals can be received in the case of the transmitter-receiver distance of about 25 km,sounding curves show no near field effect,and effective exploration depth can reach 3 km.The 2D inversion results are roughly consistent with drilling results,indicating that the high-power tensor CSAMT can be used to achieve nearly actual characteristics of underground electrical structures.Therefore,this method has great potential for application in deep geophysical exploration in plateaus and mining areas with complex terrain and strong interference,respectively.This study not only serves as important guidance on the prospecting in the Qinghai-Tibet Plateau but also can be used as positive references for deep mineral exploration in other areas.

The Kiloton Class Jiaojia Gold Deposit in Eastern Shandong Province and Its Genesis

The recent deep prospecting results in the Jiaojia area of Eastern Shandong Province indicate that the Jiaojia ore field composed of several individual gold deposits as previously suggested is actually an ultra-large gold deposit.This deposit covers an area of ～40 km2,and shows a structural control by the Jiaojia fault and its secondary faults.Gold orebodies generally occur along the same mineralization-alteration belt,and the main orebodies intersect with each other or exhibit a parallel or overlapping distribution.This deposit＇s reserves are estimated to be 1,200t of gold,being the first gold deposit of more than 1000t gold reserves in China.The No.Ⅰ-1 orebody in the Shaling-deep Sizhuang ore blocks holds gold reserves greater than 350 t,or 29 percent of the total reserves,followed by the No.Ⅰ orebody in Matang-Jiaojia ore blocks with exceeding 150t gold reserves.This deposit mainly occurs in the footwall of the Jiaojia fault,and presents zoned patterns in mineralization,alteration and structures.The strongly mineralized zones agree with strongly altered and tectonically fractured zones.These orebodies display strataform-like,veinlike or lenticular shapes,and generally show characteristics of pinching out and reappearing,branching and converging,expanding and shrinking.The orebodies commonly occur along positions where the fault strike changes and in gentle locations with dips changing from steep to gentle.The main orebodies are parallel to the main plane of the orecontrolling fault,and tend to be gentle from the surface to the deep.The orebodies mainly plunge to the southwest,with plunge angle of 45°-606° Orebodies near the main plane of the ore-controlling fault have more gold resource than those away from main fault zone.The slant depth of orebodies is generally larger than the length along its strike direction; orebodies become thick and gold grades become low from the shallow area to the deep area.Ore-forming fluids are H2O-CO2-NaCl±CH4 type with medium-temperature and moderate to low salinity.Sulfur isotopic values （δ34SCDT） for gold ores range between 11.08‰ and 12.58‰,indicating mixed sulfur sources; hydrogen isotopic values （δDVSMOW） range from-83.68‰ to-116.95‰ and oxygen isotopic values （δ18OV-SMOW） range between 12.04‰ and 16.28‰.The hydrogen and oxygen isotopes suggest that ore-forming fluids originated from primary magma,and mixing with a large amount of atmospheric water during the late stage.The Eastern Shandong Province gold deposits are associated with magmatic activities which have mantle crust-mixed source,and also share some similarities with orgenic and epithermal hydrothermal golddeposits.Because Eastern Shandong Province gold deposits with unique metailogenic features and formation setting which are different from other gold deposit types in the world,we call it the Jiaojiatype gold deposits.The kiloton class Jiaojia gold deposit is related to fluid activities,extension and detachment resulted from thermal upweiling of magmas.The strong magmatic activities in the middle to late stage of early Cretaceous in Eastern Shandong Province lead to active fluids,and provided abundant ore-forming materials for gold depsoits.Moreover,many extensional structures resulting from crustal extension provided favourable space for orebody positioning.

Geology and mineralization of the Sanshandao supergiant gold deposit(1200 t)in the Jiaodong Peninsula,China:A review

The Jiaodong Peninsula in Shandong Province,China is the world’s third-largest gold metallogenic area,with cumulative proven gold resources exceeding 5000 t.Over the past few years,breakthroughs have been made in deep prospecting at a depth of 500‒2000 m,particularly in the Sanshandao area where a huge deep gold orebody was identified.Based on previous studies and the latest prospecting progress achieved by the project team of this study,the following results are summarized.(1)3D geological modeling results based on deep drilling core data reveal that the Sanshandao gold orefield,which was previously considered to consist of several independent deposits,is a supergiant deposit with gold resources of more than 1200 t(including 470 t under the sea area).The length of the major orebody is nearly 8 km,with a greatest depth of 2312 m below sea level and a maximum length of more than 3 km along their dip direction.(2)Thick gold orebodies in the Sanshandao gold deposit mainly occur in the specific sections of the ore-controlling fault where the fault plane changes from steeply to gently inclined,forming a stepped metallogenic model from shallow to deep level.The reason for this strong structural control on mineralization forms is that when ore-forming fluids migrated along faults,the pressure of fluids greatly fluctuated in fault sections where the fault dip angle changed.Since the solubility of gold in the ore-forming fluid is sensitive to fluid pressure,these sections along the fault plane serve as the target areas for deep prospecting.(3)Thermal uplifting-extensional structures provide thermodynamic conditions,migration pathways,and deposition spaces for gold mineralization.Meanwhile,the changes in mantle properties induced the transformation of the geochemical properties of the lower crust and magmatic rocks.This further led to the reactivation of ore-forming elements,which provided rich materials for gold mineralization.(4)It can be concluded from previous research results that the gold mineralization in the Jiaodong gold deposits occurred at about 120 Ma,which was superimposed by nonferrous metals mineralization at 118‒111 Ma.The fluids were dominated by primary mantle water or magmatic water.Metamorphic water occurred in the early stage of the gold mineralization,while the fluid composition was dominated by meteoric water in the late stage.The S,Pb,and Sr isotopic compositions of the ores are similar to those of ore-hosting rocks,indicating that the ore-forming materials mainly derive from crustal materials,with the minor addition of mantle-derived materials.The gold deposits in the Jiaodong Peninsula were formed in an extensional tectonic environment during the transformation of the physical and chemical properties of the lithospheric mantle,which is different from typical orogenic gold deposits.Thus,it is proposed that they are named“Jiaodong-type”gold deposits.