【作者】 李雪梅；

【导师】 孙丰月；

【作者基本信息】 吉林大学 ， 矿产普查与勘探， 2009， 博士

【摘要】 辽东-吉南地区是我国重要的硼矿产地,硼矿床自西向东沿营口-凤城-宽甸-集安一线呈带状分布,构成世界知名的辽东-吉南硼矿带。本次研究发现辽东-吉南地区古元古代并不存在统一大陆裂解形成的辽吉裂谷,而是两个经历了不同地质构造演化历史的陆块被古大洋分隔,本文称之为“辽吉洋”。针对前人提出的“辽吉花岗岩”进行研究,发现辽吉花岗岩共有两期,本文对其中的斜长花岗岩进行了SHRIMP锆石U-Pb定年,获得1877±5Ma的年龄,通过岩相学、岩石地球化学和构造环境的研究,确定该花岗岩为碰撞花岗岩,并认为这是辽东-吉南地区古元古代晚期辽吉洋封闭、南北陆块碰撞拼贴的时间。在此基础上,总结了辽东-吉南地区动力学演化过程。本次研究获得含硼岩系中电气变粒岩的SHRIMP锆石U-Pb年龄为2179±3Ma,精确厘定了硼矿床的形成时代为古元古代。并根据年龄值判断两期辽吉花岗岩均非含硼岩系的基底,而是侵入到含硼岩系之内。通过地质地球化学研究,论证了电英岩为热水沉积岩,辽东-吉南硼矿带内的硼矿床为热水喷流沉积成因。总结了成矿规律,建立了成矿模式,开展了成矿远景预测,圈定出6个成矿远景区。更多还原

【Abstract】 The eastern Liaoning and southern Jilin provinces constitute an important borate resource area, in which borate deposits are distributed in Paleoproterozoic strata as a zone from west Yingkou to east Fengcheng, Kuandian and Jian. Former researchers considered the region to be a Paleoproterozoic rift which was formed by splitting of an Archean Craton, and the borates were deposited in a continental rift. Based on systematic comparison, the author considered that there was no Archean continental craton in the region, instead of two cratons that have different evolution and were separated by an early proterozoic ocean, to which we named as Liao-Ji Ocean.Previous studies believed that an line of important evidence of existence of Liao-Ji rift was“the bimodal volcanic rocks”. The bimodal volcanic rocks were composed of basic ones and acidic ones in borate bearing rock series. In this paper, the author has studied the tectonic settings of two types of volcanic rocks, it has been found that the basic volcanic rocks formed in the mid-ocean ridges and oceanic island, while the acidic ones formed in an island arc or a continental margin arc. Therefore they are not the so-called“bimodal volcanic rocks”in the rift setting, which suggested that there was no Paleoproterozoic Liao-Ji rift formed by splitting of an unified continent in eastern Liaoning and southern Jilin provinces.As to the so called“Liao-Ji granite”, we have carried out systematic geological and geochemical studies. It has found that there were two phases of“Liao-Ji granite”, namely the streak-like granite with age of nearly 2160Ma, and plagioclase granite, porphyritic granite and amphibolite augite syenite with ages of 1877Ma to 1850Ma. According to analysis of a systematic petrogeochemistry studies on the plagiogranite, it has been proposed that the plagiogranite was a syn-collision orogenic granite.whose ages of the plagiogranite is 1877±5Ma by SHRIMP Zircon U-Pb dating. It is distinguished that the Paleoproterozoic Liao-Ji ocean crust had been being subducted to the Archean continents both north and south towards before that age, the collisional orogenic movement happened in nearly 1877Ma, and then a continent craton formed in eastern Liaoning and southern Jilin provinces. Based on this basis, the author summarized that Eastern Liaoning-Southern Jilin Borate Ore Belt experienced geodynamic evolution of the following four stages: Anshan cycle—the north and south Archean continents formation stage;Liaohe cycle—Liao-Ji ocean evolution and closure stage; Yanliao-Hercynian cycle—plateform stabilization stage; Indosinian-Yanshan cycle—tectonic and magmatic activation stage. It was thought that the eastern Liaoning-southern Jilin Borate deposits formed in Liaohe cycle.In order to determine the formation era of borate deposit, we acquired the age of Tourmaline Leptynite in the borate bearing rock series as 2179±3Ma by the method of SHRIMP Zircon U-Pb dating, so the accurate era that borate deposits formed is Paleo-Proterozoic. At the same time, based on the dating value, it was determined that these two phases of“Liao-Ji granite”were not the basement of the borate bearing rock series, but rock bodies which penetrated into the borate bearing rock series.Through discussing the 4 typical Borate deposits of Houxianyu, Wengquangou, Yangmugan and Gaotaigou, it was found that borate deposits in the region belong to the same genesis of sedimentary exhalative, and they underwent regional metamorphism and thermal fluid alteration.Tourmalite are wall rocks which were closer to ore bodies in the borate bearing rock series. After studying of mineralogy, petrology and geochemistry, it was considered that the tourmalite have clear striped-banded structure after alteration of metamorphism, so their original rocks should be sedimentary rocks. The north American shale-normalized REE patterns of tourmalite are clearly both left inclination and represent to a typical exhalite.The borate deposits are closely relate to the tourmalite, according to borate isotopic characters, it was concluded that the borate deposits and tourmalite are both formed during sedimentary exhalative mineralizations, and the deposits in the region are typical sedimentary exhalative deposits.After studying the Fluid inclusions of tourmalite at Houxianyu borate deposit and quartz veins at Wengquangou borate deposit, it was found that there are only gas-liquid inclusions captured during sedimentary exhalative mineralization. But the fluid inclusions captured by hydrothermal fluid have two types, one was gas-liquid two-phase, the other was gas-liquid with CO2 three-phase. The homogenization temperature of fluid inclusions captured during sedimentary exhalative mineralization is 146~249℃, the salinity is 15.9~18.4%NaCl, and density is 0.96~1.04g/cm3; while the homogenization temperature of fluid inclusions of hydrothermal fluid is 142~377℃, the salinity is 12.7~14.5%NaCl, and density is 0.96~1.01g/cm3. The fluid components during sedimentary exhalative involves mainly H2O and CH4, which represent a reductive environment, but the hydrothermal stage of fluid components are mainly made of H2O and CO2.which represents oxidizing environment. Based on salinities and homogenization temperatures of fluid inclusions, we obtained pressures of sedimentary exhalative fluid are 20.11~30.99Mpa,and depths of the sedimentary exhalative deposition was 2.49km. While hydrothermal reformed pressures was 18.33~27.15Mpa,average pressure 21.92Mpa,and the quartz veins formed at the depth of 2.19km.In order to discuss the origin of the ore minerals and the fluids, the author studied the B, C, O, S isotopic data of the borate ores and ore-hosting rocks. In borate ores theδ11B value is -3.8‰~+17.4‰, which is closing to those of the Middle Ocean Ridge, so we inferred that borate must be from the Middle Ocean Ridge. The Carbon isotopic characteristics of the borate bearing serpentine marble showed that it is marine sedimentary rock. According to diagram ofδ18O-δ13C data, it was concluded that CO2 value of the serpentine marble origin from deeper magma and marine carbonate dissolution. Theδ13C value of borate ore is -2.6‰~-10.4‰,which is close to those of volcanic rocks and volcanic gases, so the carbon of borate ores has closely relationship with volcannic eruption. Theδ18O value of Borate ore is distinctly smaller than those of wall rock, so it means that the origin of the oxygen of borate ore and wall rock are different, Theδ34S value of borate ore are distinctly distributed in two ranges. Theδ34S value of pyrite is +9.80‰consistent with those of wall rock, which means that the origin of the sulfur comes from the old ocean. Theδ34S value of pyrrhotite is +1.58 to +4.16‰similar to sulfur of meteorite, which proves that the sulfur comes from volcanic eruption. This characteristic of sulfur isotope is typical characteristic of sedimentary exhalative deposits.Based on systematic studying of the dynamic evolution, typical borate deposits, exhalite, geochemistry and metallogenesis of borate deposits, we built up a metallogenic pattern of borate deposits in East Liaoning and South Jilin provinces, and summarized the metallogenic laws. Then ore prospectings were done by the author and delineated 6 prospecting areas, which may establish a stable basement for the regional mineral resource prospecting and exploration.更多还原