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.

Periodicities in the emplacement of large igneous provinces through the Phanerozoic:Relations to ocean chemistry and marine biodiversity evolution

Large igneous provinces （LIPs） are considered a relevant cause for mass extinctions of marine life throughout Earth＇s history. Their flood basalts and associated intrusions can cause significant release of SO4 and CO2 and consequently, cause major environmental disruptions. Here, we reconstruct the long-term periodic pattern of LIP emplacement and its impact on ocean chemistry and biodiversity from δ34Ssulfate of the last 520 Ma under particular consideration of the preservation limits of LIP records. A combination of cross-wavelet and other time-series analysis methods has been applied to quantify a potential chain of linkage between LIP emplacement periodicity, geochemical changes and the Phanerozoic marine genera record. We suggest a mantle plume cyclicity represented by LIP volumes （V） of V= （350-770） × 103km3sin（27πt/ 170 Ma）＋ （300-650）× 103 km3 sin（2πt/64.5 Ma ＋ 2.3） for t= time in Ma. A shift from the 64.5 Ma to a weaker -28-35 Ma LIP cyclicity during the Jurassic contributes together with probably independent changes in the marine sulfur cycle to less ocean anoxia, and a general stabilization of ocean chemistry and increasing marine biodiversity throughout the last -135 Ma. The LIP cycle pattern is coherent with marine biodiversity fluctuations corresponding to a reduction of marine biodiversity of -120 genera/Ma at 600 x 103 km3 LIP eruption volume. The 62-65 Ma LIP cycle pattern as well as excursion in -34Ssulfate and marine genera reduction suggest a not-vet identified found LIP event at - 440-450 Ma.

Nature and secular evolution of the lithospheric mantle beneath the North China Craton

The Archean mantle lithosphere beneath the North China Craton(NCC)was transformed in the Mesozoic,leading to the craton destruction.Despite the significant breakthroughs in the craton studies,lithospheric transformation mechanisms are yet to be fully understood.Compositional variations of mantle-derived rocks and xenoliths provide insights into the nature of the mantle lithosphere before and after the craton destruction.The Paleozoic lithosphere of the NCC is~200 km thick.It has a refractory mantle with an evolved isotopic signature.The Mesozoic mantle lithosphere was relatively fertile and highly heterogeneous.In the Cenozoic,the lithosphere in the eastern NCC is about 60–80 km thick.It has an oceanic-type mantle that is fertile in composition and depleted in the Sr-Nd isotopic signature.The Central Zone lithosphere is>100 km thick and has a double-layer mantle with an old upper layer and a new lower layer.The Western Block has a lithosphere of~200 km thick.The lithospheric mantle beneath the southern and northern margins and eastern part of the NCC has been transformed significantly by peridotite-melt reactions due to the multiple subductions of adjacent plates since the Paleozoic.Paleo-Pacific subduction and the associated dynamic processes significantly alter the lithosphere based on the distribution of craton destruction.The involved mechanisms include mechanical intrusion of subduction plates,melt/fluid erosion,and local delamination.The lithospheric thinning of~120 km is relevant to the continental extension caused by subduction plate rollback and trench retreat.