CAJ | 학술논문

华南西南部博白-岑溪多金属成矿带是华南地区重要成矿带。在该带中先后发现的米场、油麻坡、三叉冲等中大型钨钼矿与晚中生代白垩纪花岗岩关系密切。本文选择了该区典型岩体——三叉冲岩体进行研究,通过对其特征及成因的研究对该地区成矿作用提供指示意义。三叉冲岩体由斑状中粒黑云母花岗岩和细粒二云母花岗岩组成。LA-ICP-MS锆石U-Pb同位素定年表明,斑状中粒黑云母花岗岩形成于101~104 Ma,细粒二云母花岗岩形成于103~105 Ma。两种花岗岩都具有较大的化学成分变化,但具有相似的Nd同位素组成,εNd(t)值分别为–7.5~–6.5和–7.8~–6.7。我们认为中粒黑云母花岗岩为中元古界中-高钾玄武岩成分基底部分熔融,并与幔源基性岩浆发生岩浆混合作用形成的。在中粒黑云母花岗岩的演化过程中有角闪石+少量斜长石的分离结晶作用。细粒二云母花岗岩具有明显不同于中粒黑云母花岗岩的Na2O和K2O演化趋势；且具有更高的 CaO 和 Sr 含量；同时,细粒二云母花岗岩具有高得多的 La/Lu 比值,这些证据都表明细粒二云母花岗岩并非中粒黑云母花岗岩通过分离结晶形成的。细粒二云母花岗岩为中元古界长英质麻粒岩+少量拉斑玄武岩成分部分熔融产生中酸性岩浆,并与幔源岩浆发生混合作用形成的。幔源岩浆贡献的挥发分F使得细粒二云母花岗岩朝更富Na2O的方向演化。在细粒二云母花岗岩的演化过程中以黑云母+钾长石+斜长石的分离结晶为主。野外地质调查、岩石学及地球化学数据表明,细粒二云母花岗岩与三叉冲钨钼成矿作用的关系更为密切。晚中生代,受太平洋板块的俯冲作用的影响,桂东南地区处于拉张构造环境。软流圈上涌及玄武质岩浆底侵为基底的部分熔融提供了必要的热源,同时也为三叉冲岩体的形成提供了物质来源。華南西南部博白-岑溪多金屬成礦帶是華南地區重要成礦帶。在該帶中先後髮現的米場、油痳坡、三扠遲等中大型鎢鉬礦與晚中生代白堊紀花崗巖關繫密切。本文選擇瞭該區典型巖體——三扠遲巖體進行研究,通過對其特徵及成因的研究對該地區成礦作用提供指示意義。三扠遲巖體由斑狀中粒黑雲母花崗巖和細粒二雲母花崗巖組成。LA-ICP-MS鋯石U-Pb同位素定年錶明,斑狀中粒黑雲母花崗巖形成于101~104 Ma,細粒二雲母花崗巖形成于103~105 Ma。兩種花崗巖都具有較大的化學成分變化,但具有相似的Nd同位素組成,εNd(t)值分彆為–7.5~–6.5和–7.8~–6.7。我們認為中粒黑雲母花崗巖為中元古界中-高鉀玄武巖成分基底部分鎔融,併與幔源基性巖漿髮生巖漿混閤作用形成的。在中粒黑雲母花崗巖的縯化過程中有角閃石+少量斜長石的分離結晶作用。細粒二雲母花崗巖具有明顯不同于中粒黑雲母花崗巖的Na2O和K2O縯化趨勢；且具有更高的 CaO 和 Sr 含量；同時,細粒二雲母花崗巖具有高得多的 La/Lu 比值,這些證據都錶明細粒二雲母花崗巖併非中粒黑雲母花崗巖通過分離結晶形成的。細粒二雲母花崗巖為中元古界長英質痳粒巖+少量拉斑玄武巖成分部分鎔融產生中痠性巖漿,併與幔源巖漿髮生混閤作用形成的。幔源巖漿貢獻的揮髮分F使得細粒二雲母花崗巖朝更富Na2O的方嚮縯化。在細粒二雲母花崗巖的縯化過程中以黑雲母+鉀長石+斜長石的分離結晶為主。野外地質調查、巖石學及地毬化學數據錶明,細粒二雲母花崗巖與三扠遲鎢鉬成礦作用的關繫更為密切。晚中生代,受太平洋闆塊的俯遲作用的影響,桂東南地區處于拉張構造環境。軟流圈上湧及玄武質巖漿底侵為基底的部分鎔融提供瞭必要的熱源,同時也為三扠遲巖體的形成提供瞭物質來源。
화남서남부박백-잠계다금속성광대시화남지구중요성광대。재해대중선후발현적미장、유마파、삼차충등중대형오목광여만중생대백성기화강암관계밀절。본문선택료해구전형암체——삼차충암체진행연구,통과대기특정급성인적연구대해지구성광작용제공지시의의。삼차충암체유반상중립흑운모화강암화세립이운모화강암조성。LA-ICP-MS고석U-Pb동위소정년표명,반상중립흑운모화강암형성우101~104 Ma,세립이운모화강암형성우103~105 Ma。량충화강암도구유교대적화학성분변화,단구유상사적Nd동위소조성,εNd(t)치분별위–7.5~–6.5화–7.8~–6.7。아문인위중립흑운모화강암위중원고계중-고갑현무암성분기저부분용융,병여만원기성암장발생암장혼합작용형성적。재중립흑운모화강암적연화과정중유각섬석+소량사장석적분리결정작용。세립이운모화강암구유명현불동우중립흑운모화강암적Na2O화K2O연화추세；차구유경고적 CaO 화 Sr 함량；동시,세립이운모화강암구유고득다적 La/Lu 비치,저사증거도표명세립이운모화강암병비중립흑운모화강암통과분리결정형성적。세립이운모화강암위중원고계장영질마립암+소량랍반현무암성분부분용융산생중산성암장,병여만원암장발생혼합작용형성적。만원암장공헌적휘발분F사득세립이운모화강암조경부Na2O적방향연화。재세립이운모화강암적연화과정중이흑운모+갑장석+사장석적분리결정위주。야외지질조사、암석학급지구화학수거표명,세립이운모화강암여삼차충오목성광작용적관계경위밀절。만중생대,수태평양판괴적부충작용적영향,계동남지구처우랍장구조배경。연류권상용급현무질암장저침위기저적부분용융제공료필요적열원,동시야위삼차충암체적형성제공료물질래원。
Bobai-Cenxi polymetallic belt is an important metallic belt in South China. Several medium- to large-size tungsten deposits associated with the Cretaceous granites, such as Michang, Youmapo and Sanchachong tungsten deposits, have been found in the belt. In this paper, we choose to study the ages, chemistry and Nd isotopes of the Sanchachong pluton from the region to shed light on the petrogenesis of the pluton and relationship with associated tungsten mineralization. The Sanchachong pluton is composed of porphyritic medium-grained biotite granite and fine-grained two-mica granite. LA-ICP-MS in situ zircon U-Pb isotope data show that the porphyritic medium-grained biotite granite was emplaced at 101~104 Ma, and the fine-grained two-mica granite at 103~105 Ma. The two granites have large chemical variations, but show similar Nd isotopic compositions, withεNd(t) = –7.5~ –6.5 and –7.8~ –6.7, respectively. We suggest that the porphyritic medium-grained biotite granite originated from a magma mixing process between felsic magma derived from melting of the Meso-Proterozoic medium-to-high K basaltic basement rocks and mantle-derived mafic magma, followed by fractional crystallization of hornblende + plagioclase. The fine-grained two-mica granite shows different Na2O and K2O evolution trends from the medium-grained biotite granite, and has higher CaO and Sr contents, and higher La/Lu ratios than those of the medium-grained biotite granite. These evidences indicate that the fine-grained two-mica granite was not the derivative of the medium-grained biotite granite by fractional crystallization, but being derived from melting of the Meso-Proterozoic felsic granulite with little tholeiitic basaltic basement rocks, followed by mixing with mantle-derived mafic magma. Biotite, alkali feldspar and plagioclase have played a role in the magma evolution of the fine-grained two-mica granite. Involvement of volatile F originated from the mantle resulted in the enrichment of Na2O in the evolved fine-grained two-mica granite. Field investigation, petrology and geochemistry suggest that the tungsten mineralization is genetically linked with the fine-grained two-mica granite. In late Mesozoic, SE Guangxi was in extensional tectonic settings related to the subduction of the Pacific slab. Upwelling of asthenosphere and formation of underplated basaltic magma triggered partial melting of the basement rocks, forming felsic melts. The Sanchachong pluton formed from the mixing between the mafic and felsic magmas.