【作者】 高阳；

【导师】 毛景文； 叶会寿；

【作者基本信息】 中国地质科学院 ， 矿物学、岩石学、矿床学， 2014， 博士

【摘要】 近年来,在东秦岭-大别地区取得了找矿新突破,尤其在其东部的大别山地区,陆续发现了一批重要斑岩型钼矿床,新增钼资源量达300万t以上,充分显示了大别山地区的成矿潜力。千鹅冲钼矿和汤家坪钼矿是大别山地区近年来找矿勘探的重要成果,分别达到超大型和大型规模。本文以千鹅冲和汤家坪为典型矿床进行解剖,并结合前人资料,初步探讨了大别山地区中生代钼成矿规律及与白垩纪岩浆作用的耦合关系,取得了以下主要认识：1、对千鹅冲钼矿和汤家坪钼矿进行了详细的野外地质调查,查明了矿体特征、矿物组成及矿石组构、围岩蚀变类型及分带特征,并且详细划分了成矿阶段。两个矿床矿石中的硫主要来自岩浆,且与东秦岭-大别钼矿带内其他斑岩型钼矿床具有类似的硫同位素组成特征。2、首次对千鹅冲隐伏岩体中的二长花岗岩和花岗斑岩进行SHRIMP锆石U-Pb测年,确定其形成时代分别为130±2Ma和129±2Ma,同时运用辉钼矿Re-Os测年方法对成矿时代进行了更精确的厘定,年龄为129.4±1.5Ma。以上结果表明千鹅冲钼矿床的岩浆-成矿作用发生在约130-128Ma这样一个较窄的时限内。对汤家坪花岗岩的成岩时代进行了重新厘定,获得年龄为115±1Ma。这一结果比前人获得的年龄(121.6±4.6Ma)精度更高且更接近其成矿时代,说明其更能够代表汤家坪花岗斑岩的成岩时代。3、千鹅冲花岗岩属Ⅰ型花岗岩,其最有可能来源于下地壳超高压榴辉岩的部分熔融,同时混入一定量类似崆岭杂岩的古元古代-太古代的扬子克拉通地壳物质。千鹅冲钼矿中与成矿关系更为密切的花岗斑岩具有比二长花岗岩较低的Ce4+/Ce3+比值,表明岩浆的氧逸度不是控制其钼成矿的决定因素。4、对汤家坪钼矿床成矿岩体的岩石成因类型进行了详细的厘定。对采自汤家坪钼矿成矿岩体边部几个钻孔中的新鲜未蚀变花岗岩样品的研究表明,汤家坪花岗斑岩为铝质A型花岗岩,并带有一些(与Ⅰ型花岗岩)过渡性特征。汤家坪花岗斑岩与其附近的商城-达权店花岗岩具有不同的源区和成因。汤家坪花岗斑岩起源于闪长质岩石在0.4-0.8GPa压力条件下的部分熔融,岩浆形成深度大约为14-28km,其原岩最有可能是北大别片麻岩,且混入一定量的富集地幔。商城-达权店花岗岩与大别造山带其他高Sr/Y花岗岩具有类似的源区和成因机制,可能为加厚的榴辉质下地壳的部分熔融。5、130Ma左右,千鹅冲钼矿床下部仍存在加厚的榴辉质下地壳,热的软流圈物质的底侵引发了千鹅冲花岗岩的原岩在下地壳层位的部分熔融。130Ma之后,下地壳的拆沉导致软流圈地幔物质快速上涌,在大规模地壳伸展背景下,汤家坪铝质A型花岗质岩浆在低压、相对贫水和高温等物理化学条件下形成,并在115-113Ma左右形成汤家坪花岗斑岩及钼矿床。6、大别山地区钼矿床成矿时代上表现为白垩纪成矿的特点,空间分布上表现为沿NWW向呈带状分布在大别山北麓,其展布与区域性断裂带一致。大别山钼成矿作用与白垩纪花岗质岩浆作用密切相关,钼矿床类型以斑岩型为主。钼矿床的形成明显受断裂控制,断裂的交汇部位是成矿的有利区域。下地壳拆沉、软流圈物质上涌和大规模地壳伸展是控制千鹅冲和汤家坪钼矿成岩成矿的主要动力学机制。更多还原

【Abstract】 In recent years, the breakthroughs of prospecting have been achieved in the East Qinling-Dabie area. Especially in the Dabie area, the eastern part of the East Qinling-Dabie area, a number of large-scale porphyry Mo deposits have been discovered. The additional resources of molybdenum are more than3,000,000t, which fully demonstrated the potential of mineralization in the Dabie area. The giant Qian’echong and the large Tangjiaping Mo deposits are important achievements of prospecting and exploration in Dabie area in recent years. In this paper, we chose the Qian’echong and the Tangjiaping Mo deposits as the typical deposits to dissect. Combined with previous studies, we preliminary describe the Mesozoic Mo mineralization discipline and the relationship between the Mesozoic magmatism and the Mo mineralization. Major conclusions can be summarized as following:1. Detailed field geological survey has been carried out in the Qian’echong and the Tangjiaping Mo deposits. We identified the characteristic of the ore bodies, mineral species, ore texture and structure, wall rock alteration types and zones, and also detailed divided the mineralization stages. The sulfur in the both two deposits is mainly from magma. The sulfur isotopic compositions in these two deposits are similar to other porphyry Mo deposits in the East Qinling-Dabie Mo belt.2. SHRIMP zircon U-Pb analyses of Monzogranite and granite porphyry in the concealed stock were done in this study by first time. This analyses yielded ages of130±2Ma for Monzogranite and129±2Ma for granite porphyry. Furthermore, we report the more precise Mo mineralization age, with the molybdenite Re-Os result of129.4±1.5Ma. The above results propose that magmatism and mineralization in the Qian’echong deposit took place during a relatively short interval from130to128Ma. We determined the age of the Tangjiaping granite again, and got the age of115±1Ma. This result is more precise than the previous study (121.6±4.6Ma) and is close to the age of mineralization, and could represent the formation age of the Tangjiaping granite.3. The Qian’echong granites are belong I-type granites. The Qian’echong granites are most likely to derive by partial melting of ultrahigh pressure eclogites at lower crustal levels, and that some Paleoproterozoic-Archean YC crust, such as Kongling complex, has been incorporated into the Qian’echong granites. The granite porphyry, which is more likely related to Mo mineralization, have lower Ce4+/Ce3+than the monzogranite, suggesting oxygen fugacity is not the unconditional factor that control the Mo mineralization.4. Detailed determination of genetic type of the ore-forming granite in the Tangjiaping deposit has been undergone. We studied the fresh and unaltered granites, which sampled from drill cores distributed in the edge of the ore-forming stock. The Tangjiaping granites are belong metaluminous A-type granites, with some transitional characteristics (to I-type granites). The Tangjiaping granites and nearby Shangcheng-Daquandian granites have different source rocks and origin. The Tangjiaping granites derived by partial melting of diorite at the pressure of0.4-0.8GPa, with the corresponding depth of14-28km. The source rocks of the Tangjiaping granites are most likely to be the NDC gneiss, with some enriched mantle. The Shangcheng-Daquandian granites have the same source rocks and origin with other high Sr/Y granites in the Dabie orogen, which might derived from partial melting of thickened eclogitic lower crust. 5. At ca.130Ma, the thickened eclogitic lower crust still exist beneath the Qian’echong deposit. Underplating of hot asthenosphere material triggered partial melting of the source rocks of the Qian’echong granites at lower crustal levels. After130Ma, delamination or foundering of eclogitic lower crust caused the rapid upwelling of asthenosphere material. In the setting of large-scale crustal extension, the Tangjiaping metaluminous A-type magma formed under the conditions of low-pressure, relative poor-water, and high-temperature. Then the Thangjiaping granite and porphyry Mo deposit formed at115-113Ma.6. The mineralization ages of the Mo deposits in the Dabie orogen are almost Cretaceous. In terms of spatial distribution, the Mo deposits occurred as a NWW-trending belt along the regional faults in the northern Dabie. The Mo mineralization closely related to the Cretaceous granitic magmatism. The porphyry-type is the main type of the Mo deposits in the Dabie orogen. The formation of the Mo deposits obviously controlled by faults, and intersection sites of faults in favor of the formation of the Mo deposits. The delamination of lower crust, asthenosphere upwelling, and large-scale crustal extension are main dynamic mechanism, which controlled the mineralization and magmatism in the Qian’echong and Tangjiaping Mo deposits.更多还原