Xinlu volcanic basin is not only a significant base for uranium production but also the only uranium ore district for exploration in Zhejiang Province at present. In order to make a breakthrough in uranium prognoses, thernauthors explained the formation mechanism of uranium deposits based on studying the hotspot action in the study area so as to gain confidence in finding concealed deep uranium resources. According to the geophysical deep profile, the relatively low velocity fluid occurs at the depth of -40 km, and the relatively high-velocity magma intrusion occurs in upper strata; there are four magmatic cycles from Mesozoic in the study area; there are also three tiers of stratigraphic configuration showing the obvious hotspot action with the lower tier being metamor-phic basement, the middle tier being slippage strata, and the upper tier being lava and Cretaceous sediments. An analysis of fluid inclusions indicates that the metalbgenic hydrothermal temperature is 317 ～ 420℃, salinity ω(NaCleq) is 39.76%～49.68%, and the hydrothermal fluid is composed of CO,OH- , H2O, halogen, N2, metal elements suggesting features of mantle fluid. Metallogentic hydrothermal fluid originated from the upper mantle or the lower crust, as evidenced by an analysis of trace elements and sulfur isotopes associated with uranium element. The hotspot metallogenesis occurred here. An integrated geophysical and geochemical investigation was made and, on such a basis, a model of hotspot action in the study area was established. There are four aspects reflecting uranium metallogenesis controlled by the hotspot: (1) basic magma in deep melts partially with salic rock formed acid magma, which then erupted and resulted in the formation of Xinlu volcanic basin or in-trudeed and resulted in the generation of secondary volcanic rock and acid intrusive rock. All of these products would provide favorable strata or wall rock for metallogenesis; (2) To some extent, a series of faults occurred as a result of mantle plume, which were U-bearing hydrothermal transferring structure or storing structure of -mineralization in the process of uranium metallogenesis; (3) Part of uranium was extracted from altered wall rock, resulting from heat energy due to the upheaval of the mantle plume; (4) The concentration of useful components increased in magma because of differentiation, thus providing the metallogenic material.%新路火山岩盆地是浙江省重要的产铀基地.文章通过对该区热点作用的研究,解释了该区铀矿床(点)的形成机制,以期获得该区铀矿找矿的新突破.地球物理资料显示,该区深部40km处存在相对低速体的塑性体(地幔柱冠状体之上的幔枝构造),在其上部地层存在相对高速体的岩浆侵入体；中生代以来发育4次岩浆旋回；地层结构表现出下部为变质基底,中部为滑脱层,上部为上叠火山岩和白垩纪沉积盆地的三层式结构.热点作用的地质、地球物理特征明显.流体包裹体研究表明,成矿热液的温度为317 ～ 420℃,盐度w(NaCleq)为39.76％～49.68％,其成分为CO2及含碱、H2O、卤素、氮和一些金属元素,地幔流体特征明显,与铀矿伴生的微量元素及成矿同期的硫同位素也指示出成矿流体来源于上地幔或下地壳.地球物理和地球化学特征均指示出该区存存热点成矿作用,据此建立了该区的热点活动模式.文章认为,热点对该区铀成矿的控制主要表现为:①当深部基性岩浆运移至上地壳时,使硅铝质岩石发生部分熔融,形成酸性岩浆,喷出地表形成了新路火山岩,侵入时则形成次火山岩体和各类酸性侵入岩体,为成矿准备了有利的赋矿层位或有利围岩；②地幔柱上隆作用,形成或复活了一系列断裂构造,完善或形成了成矿所需的导矿构造和储矿构造；③地幔柱上隆时,提供了成矿所需的大量热能,造成围岩蚀变,从而萃取了围岩中的部分铀源；④随着酸性岩浆的不断分异结晶,岩浆中有用组分浓度不断增高,提供了深部热液中的成矿物质.
展开▼
