大地构造与成矿学
大地構造與成礦學
대지구조여성광학
Geotectonica et Metallogenia
2015年
5期
855-865
,共11页
杨红梅%刘重芃%段瑞春%顾晓敏%卢山松%谭娟娟%蔡应雄%张利国%邱啸飞
楊紅梅%劉重芃%段瑞春%顧曉敏%盧山鬆%譚娟娟%蔡應雄%張利國%邱嘯飛
양홍매%류중봉%단서춘%고효민%로산송%담연연%채응웅%장리국%구소비
Rb-Sr同位素%Sm-Nd同位素%闪锌矿%方解石%卜口场铅锌矿床
Rb-Sr同位素%Sm-Nd同位素%閃鋅礦%方解石%蔔口場鉛鋅礦床
Rb-Sr동위소%Sm-Nd동위소%섬자광%방해석%복구장연자광상
Rb-Sr isotope%Sm-Nd isotope%sphalerite%calcite%Bokouchang Pb-Zn deposit
因铅锌矿床的定年一直比较困难,关于黔东铅锌矿带的时代和成因认识较为混乱。本文对位于该成矿带赋存于下寒武统清虚洞组藻灰岩中的贵州铜仁卜口场铅锌矿床开展了闪锌矿Rb-Sr与方解石Sm-Nd同位素定年。矿石光薄片显示方解石和不透明矿物沿网状裂隙充填交代。用于定年的方解石,部分与方铅矿沿着同一闪锌矿细脉充填,部分沿方铅矿细脉充填,表明方解石晚于闪锌矿形成,可能属于成矿期后期产物。获得闪锌矿矿物 Rb-Sr 等时线年龄466±13 Ma (MSWD=2.0)和闪锌矿矿物+弱酸提取相+硫化物相Rb-Sr等时线年龄483±9 Ma(MSWD=8.0),二者在误差范围内一致,应代表了该铅锌矿床的主成矿期。获得方解石Sm-Nd等时线年龄422±48 Ma(MSWD=0.71),可能代表了同一成矿作用的后期阶段。即卜口场铅锌矿床后期改造成矿作用可能存在早奥陶世(483~466 Ma)和早志留世(~422 Ma)两个阶段。闪锌矿和闪锌矿分相Rb-Sr等时线对应的初始87Sr/86Sr比值分别为0.70920和0.70908,方解石Sm-Nd等时线对应的初始143Nd/144Nd比值为0.511520(εNd(t)为–11.2),指示其流体来源具有Sr、Nd富集特征,为成矿流体主要是地层封存水与区域热液流体提供了佐证。
因鉛鋅礦床的定年一直比較睏難,關于黔東鉛鋅礦帶的時代和成因認識較為混亂。本文對位于該成礦帶賦存于下寒武統清虛洞組藻灰巖中的貴州銅仁蔔口場鉛鋅礦床開展瞭閃鋅礦Rb-Sr與方解石Sm-Nd同位素定年。礦石光薄片顯示方解石和不透明礦物沿網狀裂隙充填交代。用于定年的方解石,部分與方鉛礦沿著同一閃鋅礦細脈充填,部分沿方鉛礦細脈充填,錶明方解石晚于閃鋅礦形成,可能屬于成礦期後期產物。穫得閃鋅礦礦物 Rb-Sr 等時線年齡466±13 Ma (MSWD=2.0)和閃鋅礦礦物+弱痠提取相+硫化物相Rb-Sr等時線年齡483±9 Ma(MSWD=8.0),二者在誤差範圍內一緻,應代錶瞭該鉛鋅礦床的主成礦期。穫得方解石Sm-Nd等時線年齡422±48 Ma(MSWD=0.71),可能代錶瞭同一成礦作用的後期階段。即蔔口場鉛鋅礦床後期改造成礦作用可能存在早奧陶世(483~466 Ma)和早誌留世(~422 Ma)兩箇階段。閃鋅礦和閃鋅礦分相Rb-Sr等時線對應的初始87Sr/86Sr比值分彆為0.70920和0.70908,方解石Sm-Nd等時線對應的初始143Nd/144Nd比值為0.511520(εNd(t)為–11.2),指示其流體來源具有Sr、Nd富集特徵,為成礦流體主要是地層封存水與區域熱液流體提供瞭佐證。
인연자광상적정년일직비교곤난,관우검동연자광대적시대화성인인식교위혼란。본문대위우해성광대부존우하한무통청허동조조회암중적귀주동인복구장연자광상개전료섬자광Rb-Sr여방해석Sm-Nd동위소정년。광석광박편현시방해석화불투명광물연망상렬극충전교대。용우정년적방해석,부분여방연광연착동일섬자광세맥충전,부분연방연광세맥충전,표명방해석만우섬자광형성,가능속우성광기후기산물。획득섬자광광물 Rb-Sr 등시선년령466±13 Ma (MSWD=2.0)화섬자광광물+약산제취상+류화물상Rb-Sr등시선년령483±9 Ma(MSWD=8.0),이자재오차범위내일치,응대표료해연자광상적주성광기。획득방해석Sm-Nd등시선년령422±48 Ma(MSWD=0.71),가능대표료동일성광작용적후기계단。즉복구장연자광상후기개조성광작용가능존재조오도세(483~466 Ma)화조지류세(~422 Ma)량개계단。섬자광화섬자광분상Rb-Sr등시선대응적초시87Sr/86Sr비치분별위0.70920화0.70908,방해석Sm-Nd등시선대응적초시143Nd/144Nd비치위0.511520(εNd(t)위–11.2),지시기류체래원구유Sr、Nd부집특정,위성광류체주요시지층봉존수여구역열액류체제공료좌증。
The West Hunan-East Guizhou Pb-Zn mineralization belt has great prospecting potential, however, the metallogenetic epoch and genesis are actively debated due to the difficulty in dating Pb-Zn deposits, which is the key problem affecting the further mineralization research and mineral exploration. The Bokouchang Pb-Zn deposit in Tongren, Guizhou province situates in this belt and occurs in the algal limestones of the lower-Cambrian Qingxudong Formation. Ore-formation age of the deposit is dated by sphalerite and calcite Rb-Sr and Sm-Nd isotopic isochron method. Calcite aggregates in the ore samples have net-veined, spotted and patch distributions, and have no intercalated or dissected relationship with orebody or ore vein. Micrographs of the thin sections and polished sections of the ore samples show that the calcites and opaque minerals fill and metasomatize the network fissure. The calcites used for dating are cavity fillings in the sphalerite and galena veinlets, which shows that the calcite formed after sphalerite and maybe belong to the later stage mineralization. The Rb-Sr isochrone age of sphalerite is 466±13 Ma (MSWD=2.0), while for sphalerite, diluted acid leachates and sulfide residues the age is 483±9 Ma (MSWD=8.0). The results are consistent within the error and should represent the main mineralization epoch. Calcites define a Sm-Nd age of 422±48 Ma (MSWD=0.71) with a larger error due to only four data points and the small variation ranges of 147Sm/144Nd and 143Nd/144Nd, which may indicate the later stage of mineralization according to the occurrence of the calcites. Hence, the Bokouchang Pb-Zn deposit might have undergone two stages of mineralization, the early-Ordovician and early-Silurian, which may be mainly related to the regional Caledonian movement. The initial 87Sr/86Sr ratios, corresponding to the Rb-Sr isochrons for sphalerites and their step-dissolved phases, are 0.70920 and 0.70908, respectively. They are close to or slightly higher than those of carbonate formation and the coeval seawater. The initial 143Nd/144Nd ratio, corresponding to the Sm-Nd isochron for calcites, is 0.511520 with itsεNd(t) being-11.2. These initial 87Sr/86Sr and 143Nd/144Nd ratios indicate that the fluids were mainly derived from the formation water and regional hydrothermal fluid.