白银厂矿田构造—岩浆—成矿动态演化模式

1、白银厂矿田构造岩浆成矿动态演化模式        以海相火山岩为特征的块状硫化物型矿床是我国铜矿床的主要工业类型。甘肃白银厂矿田地处北祁连山东部，是一个典型的规模较大的块状硫化物多金属矿田。前人已对其作过大量的研究，在矿区构造、成矿火山岩特征、火山机构、矿床成因模式、成矿规律等方面取得了重要成果。但对本区构造-岩浆-成矿的耦合关系缺乏系统认识。大量研究资料表明，海相火山岩型矿床在时域、地域上都与构造环境密切相关。因此，这个问题的解决有利于深入理解白银厂矿田成岩成矿机理和成矿规律，进一步认识北祁连造山带构造演化历史和

2、成矿规律，也有利于整个祁连山地区矿产勘查评价工作和寻找新的白银厂式块状硫化物矿床的深入开展。由于白银厂火山岩系形成于海相环境，后经多次变质作用的迭加，原岩的蚀变程度高且十分普遍，在这一过程中原岩的放射性母体和子体难以保持一个相对稳定的封闭体系，使本区含矿火山岩系及其外围火山沉积变质岩地层时代一直是一个有争议的难题，导致区内的构造运动、岩浆活动、成矿作用等主要地质事件的综合研究缺乏定年依据，从而影响了本区构造-岩浆-成矿耦合关系的研究。因此，本文首先调研了白银厂矿田区域地质背景和典型矿床地质特征，阐述了各种同位素测年法的适用性和局限性，确定了本次研究的测年方法为以锆石U-Pb法定年为主，并辅以全

3、岩Rb-Sr等时线和普通铅法。在此基础上，选择锆石为重点研究对象，利用Pupin(1980)的锆石形态群法和红外光谱系统研究了白银厂矿田锆石的标型特征、成因分类、产出环境、形成温度、变生程度，确定锆石U-Pb法采用锆石形态群法与颜色、粒度、磁性相结合的分群、分点的实验方案，采用本测年方法，厘定了白银厂矿田成岩成矿主要地质事件的地质年龄。最后，在分析锆石形成温度、变生程度、地质年龄之间内在关系的基础上，结合区域地质背景，探讨了本区岩浆来源及构造-岩浆-成矿主要地质事件的发生、发展、延续的动态演化过程，建立了白银厂矿田构造-岩浆-成矿动态演化模式。本文研究结果表明：白银厂矿田构造-岩浆-成矿动态演

4、化模式为：该区构造岩浆活动始于574.2Ma以前，由于裂解，拉张构造运动的频繁活动，地下岩浆活动异常活跃，以幔源为主的壳幔混合型岩浆沿构造断裂上侵，近地表出现强热地质变质。随着构造岩浆活动的继续，能量的积聚，458.99Ma岩浆熔岩涌出地表，揭开了本区岩浆火山活动事件的序幕。446Ma440Ma，是本区火山活动全盛时期，在本区大范围内形成有价值的多金属硫化物矿床。随后火山活动减弱，本区大规模的岩浆活动趋于结束，只有在局部地区，仍存在强度不大的岩浆活动。二叠纪全球性大规模火山活动，致使区内整个中寒武纪的火山沉积岩普遍发生变质Marine volcanic massive sulfide depo

5、sit is one of the major commercial types of copper deposit in china. The Baiyinchang orefield is a typical bigger massive sulfide polymetallic orefield, which located on the eastern part of the Qilian mountain chains. Predecessors have done a great deal of work on structure, metallogenetic volcanic

6、character, volcanic framework, genetic models of deposits, and metallogenetic laws, and all of these have been made a substantial contribution. Whereas there was not system cognition in coupling connection of tectonic-magma-mineralization. A great deal of dada show marine volcanic massive sulfide de

7、posit was closely associated with tectonic settings in temporal aspect and spatial aspect. Therefore, solved the problem was propitious to deeply apprehend mechanism of rock and ore formation and metallogenic deposit regularity, and deeply know tectonic evolvement and metallogenic deposit regularity

8、 of Qilian mountain region, also to exploration appraise expansion of Qilian mountain region and search new the style of Baiyinchang marine volcanic massive sulfide deposit.Volcanic rock system in Baiyinchang orefield was formed in marine environment with multiple metamorphism, which explains high a

9、nd general alteration, and radioactive parent and daughter could not keep relative stability closing system in the process, leaded stratum epoch of the ore bearing volcanic and outer volcanic sediment metamorphic rock was a difficult problem pendent, so geological events of tectogenesis, magmatic ac

10、tivity, metallogenesis lacked dating materials, and effected study coupling connection of tectonic-magma-mineralization.Wherefore, the first work was study area geology setting and character of type deposit of Baiyinchang orefield, and expatiate applicability and localization of diversified isotopes

11、 dating, then fixed on dating method first was U-Pb isotope and assisted Rb-Sr and Pb-Pb. Zircon typomorphic peculiarities, genetic classification, occurrence environment, metamict degree were researched using Pupin(1980) the population typology of zircon and Infra-red Spectra Analysis, and main met

12、hods of isotopic dating were confirmed by taking zircon as a principal research object. Age of main geological events and space variation regularity were determined, and Dynamic evolvement process on occurring, developing, continuing was taken to recognize the structure, magma activity and metalloge

13、nesis in the region. Lastly, found tectonic-magma-mineralization dynamic evolution pattern of Baiyinchang orefield. was that: Structure magma activity in the region had begun before 574.2 Ma. Because of frequent cracking and tensile tectogenesis and very flourish magma activity, magma in deep crust

14、up intruded along tectonic fault, then there was appeared a strong thermal metamorphism process near the earth's surface. With continuing structure magma activity and energy accumulating, magma squirted the earth's surface and initiated volcanic activity event in the region in 458.99 Ma. It

15、was floruit of volcanic activity in middle Caledonian between 446 Ma and 440 Ma. Mass volcanic rock was squirted, and ore bearing magma was risen by tectonic fissure, then formed a large-scale valuable polymetallic sulfide orefield. Then volcanic activity decreased, and mass magma activity went to end, there existed feebleness intension magma activity only in part a