CAJ | 학술논문

陕西省凤县-太白(凤太)地区位于秦岭造山带的西段,是我国重要的金属成矿集中区之一.本文重点分析凤太地区中泥盆统古道岭组与上泥盆统星红铺组过渡部位的沉积成因硅质岩.它是八方山-二里河铅锌矿床的主要赋矿层位.硅质岩多为灰黑色,块状、层纹状、角砾状构造,致密坚硬,经受过轻微变质作用(主要是重结晶作用),主要组成矿物为细晶、微晶石英,含有少量的铁白云石、方解石、绢云母、炭质.根据地球化学分析,八方山-二里河地区沉积成因硅质岩的SiO_2含量均大于80%,最高者可达95.3%,TiO_2和Al_2O_3明显偏低,高FeO,Al/(Al+Fe+Mn)值落在0.13～0.64之间.大部分微量元素含量远小于地壳元素丰度,但Ba、As、Sb、B、Ag、Hg含量较高.在V/Y-Ti/V和Ti-V图解中,硅质岩样品投影在洋中脊→大陆边缘的洋盆位置,大部分落在远洋区域,部分靠近大陆边缘.样品稀土元素含量较低,∑REE仅为3.28×10_(-6)～20.66×10_(-6),经北美页岩标准化后的稀土元素配分曲线可以分为H和S两组.H组曲线左倾,富集重稀土(HREE),具有明显的热水成因特征.S组与H组稍有差异,是受非热水沉积作用影响所致.(La/Lu)_N介于0.36～1.99,多分布于0.36～0.70和1.00～1.99两个区间内,分别代表与洋中脊环境相似的的洋盆喷口或断裂附近环境和受一定陆源物质影响的远洋盆地或深海平原环境.(La/Yb)_N值介于0.32～2.21,多分布0.32～0.72和1.74～2.21两个区间内,地质意义与(La/Lu)-N类似.硅质岩样品的(La/Ce)_N值在1.04～3.28,多数大于1,平均为1.62,主要反映大洋盆地(或深海平原)环境,个别样品也表现出大陆边缘沉积特征.研究结果表明,尽管经历了后期成岩作用等,但硅质岩仍整体上较好地保持了初始沉积时的地球化学特征.
합서성봉현-태백(봉태)지구위우진령조산대적서단,시아국중요적금속성광집중구지일.본문중점분석봉태지구중니분통고도령조여상니분통성홍포조과도부위적침적성인규질암.타시팔방산-이리하연자광상적주요부광층위.규질암다위회흑색,괴상、층문상、각력상구조,치밀견경,경수과경미변질작용(주요시중결정작용),주요조성광물위세정、미정석영,함유소량적철백운석、방해석、견운모、탄질.근거지구화학분석,팔방산-이리하지구침적성인규질암적SiO_2함량균대우80%,최고자가체95.3%,TiO_2화Al_2O_3명현편저,고FeO,Al/(Al+Fe+Mn)치락재0.13～0.64지간.대부분미량원소함량원소우지각원소봉도,단Ba、As、Sb、B、Ag、Hg함량교고.재V/Y-Ti/V화Ti-V도해중,규질암양품투영재양중척→대륙변연적양분위치,대부분락재원양구역,부분고근대륙변연.양품희토원소함량교저,∑REE부위3.28×10_(-6)～20.66×10_(-6),경북미혈암표준화후적희토원소배분곡선가이분위H화S량조.H조곡선좌경,부집중희토(HREE),구유명현적열수성인특정.S조여H조초유차이,시수비열수침적작용영향소치.(La/Lu)_N개우0.36～1.99,다분포우0.36～0.70화1.00～1.99량개구간내,분별대표여양중척배경상사적적양분분구혹단렬부근배경화수일정륙원물질영향적원양분지혹심해평원배경.(La/Yb)_N치개우0.32～2.21,다분포0.32～0.72화1.74～2.21량개구간내,지질의의여(La/Lu)-N유사.규질암양품적(La/Ce)_N치재1.04～3.28,다수대우1,평균위1.62,주요반영대양분지(혹심해평원)배경,개별양품야표현출대륙변연침적특정.연구결과표명,진관경력료후기성암작용등,단규질암잉정체상교호지보지료초시침적시적지구화학특정.
The Fengxian-Taibai area,Shanxi Province,is situated in the western section of the famous Qinling orogene,central China,with rich mineral resources.This study deals with chert from the transitional zone hetween the Gudaoling(D_2)and the Xinghongpu(D_3)formations of the Fengxian-Taihai area.The chert formation is the ore-hosting strata of the Bafangshan-Erlihe metallic deposit.The chert is mainly dark gray in color,hard and highly dense,with massive,lamellar and hreceiated sedimentary structures.It was slightly metamorphosed(mainly recrystallized).Cryptomere-crystallitic quartz is the dominant mineral of the studied chert,with small amounts of ankerite,calcite,sericite,carbon and the likes.It is shown by geochemical analysis that the studied chert is higher than 80% in content of SiO_2,with the highest reaching 95.3%,but low in contents of TiO-2 and Al_2O_3.The value of Al/(Al+Fe+Mn)ranges in 0.13～0.64.Most of trace elements are much lower in content than the Clarke value,however,Ba,As,Sb,B,Ag and Hg are higher.Plotted in the diagram of V/Y～Ti/V and Ti～V,the samples of chert fall into the ocean basin area,from mid-oceanic ridge to the oceanic margin,with most in pelagic area and part near oceanic margin area.The content of ∑ REE ranges in 3.28×10~(-6)～20.66×10~(-6).The samples of chert may be divided into two groups(H and S)based on their NASC-normalized REE distribution pattern.The group H is characterized by NASC-normalized REE distribution pattern inclining to the different from the group H,implying the eontamination of non-hydrotherma]sedimentation on hydrothermal one.The value of (La/Lu)_N is scattered in 0.36～1.99,characterized by the occurrence of two peaks in 0.36～0.70 and 1.O0～1.99.The first peak represents the environment of the vents in the oceanic basins or deep fractures in mid-oceanic ridges,while the second one denotes the environment of far ocean basin or abysmal sea plain influenced by continental sources.The value of(La/Yb)_N ranges in 0.32～2.21,with most in the two peaks of 0.32～0.72 and 1.74～2.21.(La/Yb)_N has similar geological implications to(La/Lu)_N The value of (La/Ce)Nvaries in 1.04～3.28,with an average of 1.62 and most being higher than 1.00,indicating that the chert formed mainly in oceanic basin or abysmal sea plain,partly in the continental margin.It is concluded from the present study that the original geochemical characteristics of chert are well conserved despite of later reworking.