CAJ | 학술논문

秦岭造山带南缘存在大片的早古生代基性火山岩，荞麦冲金矿的正长斑岩脉体呈北西向侵入基性火山岩地层中。本文通过对该正长斑岩脉体中的岩浆岩锆石的LA-ICP-MS U-Pb定年、元素地球化学以及Hf同位素研究，探讨正长斑岩脉体的侵入时代、岩石成因和地球动力学背景。锆石U-Pb定年结果：正长斑岩脉体的侵入时代可以分为2期，相对应的2件正长斑岩锆石206Pb/238U年龄加权平均值分别为（415±7）Ma、（477±6）Ma，前者属于晚志留世时期，后者为寒武纪到早奥陶世时期。地球化学特征上显示具较高的SiO2含量(>75%)，里特曼指数δ=1.59，高Al低Ti的特点，Eu和Sr具有明显负异常，为钙碱性脉体。正长斑岩的Hf同位素检测结果得到εHf（t）全部为正值，其变化范围较大（3.4~11.8），说明岩浆主要来自亏损地幔，个别εHf（t）异常，推断岩浆上侵过程中混入少量地壳物质，从而显示壳幔混合特征。在基性岩的地球化学表现为稀土总量很高（∑REE=149.62×10-6~321.55×10-6），轻稀土强烈富集型，呈现出高度分异的特点。研究表明，在早古生代时期，区域上为板内裂解的构造环境，使软流圈地幔上涌冷凝形成基性岩地层，正长斑岩脉体在侵入基性岩形成过程，从地壳深部的Au带入地壳表层，为地层Au的预富集，后期剪切成矿作用提供了Au的物质来源；正长斑岩脉体形成时代的厘定，确定了该区金源层形成时代，对后期金的富集具有重要意义。
진령조산대남연존재대편적조고생대기성화산암，교맥충금광적정장반암맥체정북서향침입기성화산암지층중。본문통과대해정장반암맥체중적암장암고석적LA-ICP-MS U-Pb정년、원소지구화학이급Hf동위소연구，탐토정장반암맥체적침입시대、암석성인화지구동역학배경。고석U-Pb정년결과：정장반암맥체적침입시대가이분위2기，상대응적2건정장반암고석206Pb/238U년령가권평균치분별위（415±7）Ma、（477±6）Ma，전자속우만지류세시기，후자위한무기도조오도세시기。지구화학특정상현시구교고적SiO2함량(>75%)，리특만지수δ=1.59，고Al저Ti적특점，Eu화Sr구유명현부이상，위개감성맥체。정장반암적Hf동위소검측결과득도εHf（t）전부위정치，기변화범위교대（3.4~11.8），설명암장주요래자우손지만，개별εHf（t）이상，추단암장상침과정중혼입소량지각물질，종이현시각만혼합특정。재기성암적지구화학표현위희토총량흔고（∑REE=149.62×10-6~321.55×10-6），경희토강렬부집형，정현출고도분이적특점。연구표명，재조고생대시기，구역상위판내렬해적구조배경，사연류권지만상용냉응형성기성암지층，정장반암맥체재침입기성암형성과정，종지각심부적Au대입지각표층，위지층Au적예부집，후기전절성광작용제공료Au적물질래원；정장반암맥체형성시대적전정，학정료해구금원층형성시대，대후기금적부집구유중요의의。
On the southern margin of the Qinling orogenic belt, there exists a multitude of Early Paleozoic mafic volcanic rocks, and the syenite porphyry veins in the Qiaomaichong gold deposit were intruded in NW direction into mafic volcanic rocks in the study area. By means of studying new zircon LA-ICP-MS U–Pb age and Hf-isotope, whole-rock major and trace elements of syenite porphyry veins in the Qiaomaichong gold deposit and the mafic country rock, the authors tried to constrain the age and petrogenesis and geodynamic background of the siliceous veins. It is revealed that the intrusion of the syenite porphyry can be divided into two phases, and the corresponding two zircon samples of syenite porphyry have 206Pb/ 238U weighted average ages of (415 ± 7) Ma and (477±6) Ma respectively. The former age belongs to the Late Silurian, whereas the latter to the Early Ordovician. Veins have a high SiO2 (>75%) content,σ=1.59,and A/CNK=1.28, which suggests peraluminous alkaline siliceous shear veins. TheεHf (t) values are all positive, and vary in a large range ( 3.4 to 11.8) , which suggests that almost all the matter came from the depleted mantle source, exhibiting a crust-mantle mixing feature. The mafic rocks have a high amount of REE (149.62×10-6-321.55×10-6), and are strongly enriched in light rare earth elements , showing a high degree of differentiation. Research shows that this area was within plate tectonic cleavage in the early Paleozoic, so the mantle asthenosphere upwelling of magma formed mafic rocks. Then the veins brought the Au from deep crust into the surface crust in the invasion process, thus providing material of Au sources for pre-concentration of Au and later shear mineralization. The determination of the age of the formation of veins has a great significance for the study of late stage gold enrichment.