Research On Basalt And Its Metallogenisis In Gejiu, Yunnan

The doctoral dessertation title of Research on basalt and its metallogenisis in Gejiu, Yunnan is selected based on the project ( item serial number: 2004BA615A-03 ) of tackling scientific and technic key problem of the tenth five years programming in China and the project title of Research on basalt and its metallogenisis in Gejiu ore area and its periphery Sponsored by Yunnan Tin Ltd.. The many researches on the section survey of basalt in Gejiu area;the petrology, petrochemistry and geochemistry analysis of the basalt, and the area geological synthetically study;the study of the geological characteristics of the deposit, the mineralogy, texture and structure of ores;the systematically study of the microelement, rare earth element, stable isotope and fluid inclusion and so on of rock or ore have been done. And the following conclusions have been drawn:No.1 The basalts play an important role in a formation of Gejiu tin-polymetallic ore deposits. Gejiu tin-polymetallic ore deposits have been thought as the granitic mineralization of the Yanshanian epoch in past time, however,the author finds out there are some tin ore deposits related to (ultra-) ferromagnesian rock in the word by means of consulting a wealth of relevant reference material. It's proved that basalts in Gejiu play an important role in a formation of Gejiu tin ore deposits. On the one hand, basalt of the Indo-Chinese epoch provided matter source for formation of Gejiu tin ore deposit;on the another hand, because shapes and attitude of tin-polymetallic orebodies were controlled by shapes and attitude of granite of the Yanshanian epoch and those of granite of the Yanshanian epoch were controlled by those of basalt of the Indo-Chinese epoch.In other words, shapes and attitude of tin-polymetallic orebodies were indirectly controlled by shapes and attitude of basalt of the Indo-Chinese epoch.No.2 The author has built three-dimension models of distribution of basalt and granite and protracted all kinds of isoline of distribution of basalt and granite in eastern Gejiu for the first time. The distribution of basalt and granite in eastern Gejiu is that elevation of northwest side ishigher than elevation of southeast side.No.3 The volcanism of the Indo-Chinese epoch in Gejiu is divided into three epochs according to the author's research on horizon, mineral features and mineral texture features of basalt. Basalt of epoch 1 is basalt of lower Gejiu Formation(Anisian period) ,which is distributed in Xinjiang mining, Kafang,Qibeishan,Zhuyeshan,Wanzijie,Tangzi'ao and qilinshan in eastern Gejiu. The main product of volcanism of this epoch is lava which is blastoporphyritic basalt, tremolitizated, phlogopitizated basalt, phlogopitizated , tremolitizated basalt and actinolitizated basalt. Basalt of epoch 2 is basalt of lower Falang Formation(early Ladinian period) ,which is distributed in Shuitangzhai, Baohe, Muhuaguo, and Mupuling in western Gejiu. The main product of volcanism of this epoch is tuff which is tuff with pyroclastic rock fragment and magmatic fragment and tuff with magmatic fragment and vitric fragment. Besides tuff, there is amygdaloidal basalt. Basalt of epoch 3 is basalt of upper Falang Formation(late Ladinian period-Norian period) ,which is distributed in Tabai, Heping, Nide, Deshengcong and Niushizhai in western Gejiu. The main product of volcanism of this epoch is lava which is Massive basalt, amygdaloidal basalt and pillow basalt while there being metamorphic tuff whose metamorphic grade reach schist or phyllite.No.4 The volcanism and mineralization in eastern Gejiu is divided into three stages for the first time according to the author's research on horizon feature of stratum of Gejiu Formation, petrologic feature and geochemical feature of the basalt of epoch 1. Basalt of stage 1 is basalt of lower Kafang member of Gejiu Formation(T2gi1) ,which is distributed in Xinjiang mining, Donggualin,Qianjin Mining, and lower Qibeishan. The main volcanic rock of this stage is metamorphic basalt which takes phlogopite as the main mineral while tremolite as subsidiary. Main textures basalt of this stage are palimpsest interslice texture and lepidoblastic texture. The volcanism of this stage formed some copper, gold and bismuth ore deposits, example for/Vorebody 1-9 in Kafang. Basalt of stage 2 is basalt of lower Kafang mem] of Gejiu Formation(T2gi1) ,which is distributed in upper Qibeishan/Themain volcanic rock of this stage is metamorphic basalt which takes tremolite as the main mineral while phlogopite as subsidiary. Main textures basalt of this stage are palimpsest interslice texture and nematoblastic texture. The volcanism of this stage formed some copper and tin ore deposits, example for orebody 13-2-3 in Zhuyeshan. Basalt of stage 3 is basalt of lower Kafang member of Gejiu Formation(T2gi5) ,which is distributed in Wanzijie and Tangzi'ao. The main volcanic rock of this stage is metamorphic basalt whose main minerals are actinolite and tremolite and whose main textures are palimpsest intersertal texture, palimpsest tholeiitic texture and nematoblastic texture. The volcanism of this stage formed some copper and tin, copper ,lead, zinc and silver ore deposits, example for orebody 5 in Wanzijie.No.5 The author has firstly put forward a new viewpoint about evolution of chemical ingredient of basalt of the Indo-Chinese epoch in Gejiu which is from high potassium-rich basalt, potassium-rich basalt to natrium-rich basalt. It is proved that basalts of three epoch are alkali-basalt according to the author's work about petrochemistry of basalt in Gejiu. From the early to the late, the sequence of evolution is high potassium-rich basalt, potassium-rich basalt and natrium-rich basalt.No.6 It is proved that formation of Gejiu tin ore deposit is related to the volcanism of the Indo-Chinese epoch in a certain degree. According to the research on features of microelements, lead isotopes, sulphur isotopes, mineralization dating of Pb-Pb method, Ar-Ar method and K-Ar method, rare earth elements and inclusion of basalt-type sufide deposit, basalt of the Indo-Chinese epoch provided matter source for formation of Gejiu tin ore deposit at least.Orebody 13-2-3 in Zhuyeshan and Orebody 1-9 in Kafang contact conformably with the basalt of the Indo-Chinese epoch, whose country rock is meramorphic basalt. The ores possess banded structure, whose main metallic minerals are pyrite and chalcopyrite. Copper is intimately related to tin, which shows ore-formation of copper and tin is volcanism.No.7 Guided by the hypothesis of ore-formation of basalt, new train ofthought of ore-searching are put forward, six metallogenic prognosticates and the prospecting perspective areas are pointed out.