胶东型金矿

Jiaodong-type gold deposit

胶东是全球唯一已知赋存于前寒武纪变质地体中的晚中生代巨型金矿省,其成矿系统独具特色,具体表现为:(1)位于陆内复合构造域,经历了多期重大构造-热事件,大规模金成矿作用受控于120±2Ma古太平洋板块俯冲方向变化及其诱发的软流圈上涌、岩石圈改造和伸展-挤压变形交替及控矿断裂剪压-剪张转换;(2)多重控矿构造和多样赋矿建造联合控制了不同规模和类型金矿的发育,形成了三山岛、焦家、招平、栖霞、郭即和牟乳六条NE向金矿带和三山岛-栖霞EW向富金廊带,导致了金矿化类型(焦家式/破碎带蚀变岩型、玲珑式/石英脉型、蓬家夼式/蚀变砾岩±角砾岩型、辽上式/黄铁矿-碳酸盐脉型)及其地质-地球化学特征的多样性;(3)主要矿化元素Au、Ag、Cu、Pb和Zn均达到工业利用要求,并有多种共/伴生关键金属超常富集;(4)不同金矿带中硫化物Pb同位素组成与探明金资源储量及到郯庐断裂带的距离线性相关,反映距离幔源流体主通道越近、金属硫化物中放射性成因Pb含量和幔源组分占比越多、金成矿强度越大;(5)区域总体相对均一的Δ199 Hg(平均~0.012‰)及Δ199 Hg/Δ201 Hg与金品位呈线性负相关,表明成矿物质来源于富集岩石圈地幔、且地幔被俯冲洋壳及其上覆沉积物交代的程度控制了金品位的高低;(6)区域恒定的Δ33 S同位素组成(~0‰)排除了巨量金源自太古宙变质基底及其重熔花岗岩的可能,重的δ34 S(平均9.0±3.7‰)来源于俯冲的古太平洋板片及其上覆沉积物的脱挥发份;不同金矿带Δ33 S/δ34 S与探明金资源储量及其到郯庐断裂带距离线性相关,反映成矿期地壳伸展程度控制了金成矿强度;(7)区域He-Ar和H-O同位素组成显示壳幔混合特征,焦家式金矿的成矿流体组成更靠近地幔、玲珑式金矿位于地幔与地壳过渡带;三山岛、焦家和招平金矿带的成矿流体相对接近幔源流体,而郭即金矿带具有相对开放的构造环境;不同金矿带氢-氧同位素组成和探明金资源储量正相关,可能表征了从西到东成矿流体通量和流体-岩石反应强度逐渐降低。基于对上述特征的总结,提出了胶东型金矿的成因模式,明确了其成矿地球动力学背景和深部驱动、巨量金属和流体及络合物来源、输运通道和方式、源→汇过程和机制、成矿后变化和保存等成矿系统形成的关键因素,确立了“拆离断裂系与基底活化带及幔源流体通道复合控矿”的勘查思路和“四步式”的勘查模型。综上,胶东金矿不同尺度的鉴别特征及其形成的关键因素明显不同于全球已知的其他金矿类型,难以被已有成矿模式所涵盖,属于一种新的金矿类型——胶东型,其成因模式对华北、华南、西伯利亚、西澳伊尔岗、北美怀俄明和南美圭亚那等陆内金矿床具有普适性;系列找矿突破则验证了该成因模式与勘查模型的合理性和适用性。因此,本文认为胶东型金矿是全球研究热点和重要的金矿勘查方向,而该地区找矿的主攻目标是资源量大且品位和产状稳定的破碎带蚀变岩型金矿。

Jiaodong area is the only Late Mesozoic giant gold province hosted in a Precambrian metamorphic terrane in the world.The metallogenic system of Jiaodong gold province is unique with the following distinctive features:(1)It is situated in an intracontinental composite tectonic setting which has experienced multiple tectono-thermal events.The large-scale gold mineralization is controlled by the change of the subduction direction of the Paleo-Pacific plate and induced the asthenosphere upwelling,the modification of the lithospheric mantle,the transition of the tectonic regime from compression to transpression,and the transition of ore-controlling faults from transpression to transtension regime at 120±2Ma.(2)Multiple ore-controlling structures and diverse ore-hosting formations collectively control the development of gold deposits with various scales and types,which result in the formation of six NE-trending gold belts,namely Sanshandao,Jiaojia,Zhaoping,Qixia,Guoji and Muru,together with an EW-trending gold-rich corridor,namely Sanshandao-Qixia.These belts give rise to different mineralization types of gold deposits(Jiaojia-type/altered rock type in fractured zones,Linglong-type/quartz vein type,Pengjiakuang-type/altered conglomerate±breccia type,Liaoshang-type/pyrite-carbonate vein type),and each exhibiting distinct geological-geochemical characteristics.(3)The main mineralized elements of the belt include Au,Ag,Cu,Pb and Zn,all of which meet the requirements of industrial utilization.Furthermore,it is an area with super-enrichment of many coexisting critical metals.(4)The Pb isotopic composition of gold-bearing sulfides in different gold belts is linearly correlated to the proven gold reserves and the distance to the Tanlu fault zone,suggesting that the proximity to the main channel of mantle-derived fluids leads to the more radiogenic Pb content and mantle-derived components in sulfides and higher gold mineralization intensity.(5)TheΔ199 Hg value(averaged at~0.012‰)is relatively uniform in the region,and the negative correlation betweenΔ199 Hg/Δ201 Hg and the gold grade indicate that its ore-forming fluids is derived from the metasomatic lithospheric mantle,and the intensity of mantle metasomatism by subducted oceanic slab and its overlying sediments controls the gold grade.(6)The constantΔ33 S isotopic composition(~0‰)of gold-bearing pyrites excludes the Archean metamorphic basement and its remelting granite as the initial gold source.The heavyδ34 S(averaged at 9.0±3.7‰)is attributed to the devolatilization of the subducted Paleo-Pacific plate and its overlying sediments.TheΔ33 S/δ34 S of different gold belts is linearly correlated to the known gold reserves and their distance to the Tanlu fault zone,reflecting that the degree of crustal extension during the mineralization period controls the gold mineralization intensity.(7)The regional He-Ar and H-O isotope compositions show the characteristics of crust-mantle mixing.The isotopic compositions of ore-forming fluids of the Jiaojia-type gold deposits resemble mantle value,while those of the Linglong-type gold deposits are distributed in the transition zone between mantle and crust.The Sanshandao,Jiaojia and Zhaoping gold belts exhibit fluid isotopic compositions similar to mantle-derived fluids,whereas the Guoji gold belt has a relatively open tectonic environment.Hydrogen-oxygen isotope composition positively correlates with the known gold reserves,suggesting a gradual decrease in ore-forming fluid flux and fluid-rock reaction intensity from west to east.Based on these findings,we propose a genetic model for Jiaodong-type gold deposits and clarify the key factors for the formation of the metallogenic system,such as the metallogenic geodynamic background and deep driving force,the source of giant gold and fluids and metal complexes,the channel and mode of transport,the process and mechanism of source-to-sink,the post-mineralization changes and preservation.The exploration idea of‘detachment fault system and basement activation zone and mantle-derived fluid channel composite ore-controlling’and a‘four-step’exploration model are established.The identification characteristics of different scales of Jiaodong gold deposits and the key factors of its formation are different from other types of gold deposits in the world.It is difficult to be explained by the existing metallogenic model.Thus,it belongs to a new type of gold deposit:The Jiaodong type.Its genetic model is universal for gold deposits in North China,South China,Siberia,the Yilgarn block of western Australia,Wyoming of South America,and Guyana of South America.Numerous prospecting breakthroughs validate the rationality and applicability of the genetic model and the proposed exploration model.The Jiaodong-type gold deposits emerge as a significant research focus and exploration direction,with disseminated gold deposits being the primary exploration target in Jiaodong area due to their large resources and stable occurrence.