Study On The Genetic Process Of The Shazi Independent Scandium Deposit In Qinglong County,Guizhou Province

The Shazi deposit is a newly discovered large-scale anatase deposit that was located in the Qinglong,southwestern Guizhou Province.This deposit was found in cliff debris and collapsed materials from weathered Emeishan basalt.No report yet for such a new deposit type and little research work has been done.This research aimed at investigating the ore-forming conditions,ore-forming processes,genetic mechanisms,and initial mineralization patterns for the Shazi independent Sc ore deposit,thereby can provide guidance for the exploration of new ore kinds,new ore-forming partterns and ore prospecting.On the base of the previous studies,this study is granted by the Natural Science Foundation of China“Firstly discovered Ti deposit in Guizhou-Formation Mechanism of the Shazi Anatase Deposits in Qinglong”?Grant No.41262005?.The survery region is not only an important metallogenic belt gernerating Au,Hg,As,Sb,Tl,etc,but also one of the key areas for the Emeishan hot plume research.Some previously research work provide many important information related with the rocks,strata,tectonics and ore deposits,which laid a solid foundation for this doctoral dissertations.This research focused on the geological background of the regional mineralization,the geological characteristics of the deposit and the mining area,mineral features,major and trace elements geochemical characteristics,REE geochemical characteristics,indicating significance of the U-Pb isotope characteristics,Hf isotope compositon,iron isotope characteristics,analysis of the physical and chemical conditions of mineralization,analysis of the internal geological environment of mineralization,analysis of the external geological environment of mineralization,metallogenic process research,genesis mechanism of the deposit,metallogenic model of the ore deposit,etc.The resulted contributions from the research carried out in this study on the metallogenic process of the ShaZi independent scandium deposit in Qinglong are as follows.Firstly of all,the Emeishan mantle plume activity resulted in basaltic magma eruption in early Late Permian:the hot mantle plume tectonics created mantle uplift and the mantle source materials will melt and produce mantle fluilds,which owns plenty of ore-forming materials storage,large fluid reservoir and stable heat supply.The upflit usually acts on areas where the crust-mantle interaticon is strong.The occurrence of the mantle fluilds not only bring a large number of deep mantle material into metallogenic system,but also implies the existence of a thermal environment in this region,providing favorable conditions for the continusly mineralization and the formation of large or super large ore deposit.There significances of mantle fluid mineralization include ore-forming from the fluilds and providing metallogenic material,ore-forming fluids,alkali and siliceous materials,and the heat.The mantle fluids from Emeishan mantle plume makes curst-mantle interaction and high thermal flow field,consitituting a large-scale accumulation system for metallogenic material.Under multistage dynamics,the metallogenic material from these fluids will migrate upward in gaseous form and some metal elements along with magmas will reach shallow crustal structure.Consequently,quantity of mantle or crustal source metallogenic materials will mineralize at the shallow crust or the earth's surface in the southwestern region of China.Magma is a very useful carrier in the process of material transportation.Emeishan basaltic magma is the ore-forming material source for the various ores in the sourthwest of Guizhou.Meanwhile,the geomorphologic pattern of west Guizhou is therefore high on the west-north and low on the east-south.Secondly,the special Karst depressions form a favorable geochemical barrier.Due to the Emei mantle plume activity,the formed depositional environment in Late Permian in Southwest Guizhou is mainly carbonate terrace phase and basin?ditch?phase in scattered orders.The terrace phase is composed of shallow marine carbonates,while the basin?ditch?phase is composed of deep or relatively deep water deposits of Calcium peat and volcanic debris.At the edge of some high isolated terraces,the biological carbonate rocks especially the reefs?shoal?are developed,and form a distinctive terrace-basin?ditch?deposition model in southwest Guizhou.At the end of the mamakou period in early Permian,there is widespread depositonal hiatus in sourthwest Guizhou.According to previous studies,this hiatus has been subjected to at least 400 thousand years of weathering and erosion.Because of the exposure and dissolution of carbonate rocks,an undulating Karst is formed?with little change in mining area?.The various basins in different size and with uneven bottom and meanwhile seperated by the Karst cones and colliculus indicate chemical element concentration areas resulted from different geochemical mutation zones.This complex Karst geomorphology is formed in a period of Emeishan basaltic magmatic activity,when the magma violent erupted and overflew into these basins,producing certain temperature and pressure in the basin,whereafter a relatively closed water basin with low temperature and low pressure is formed.The hydrolysis of the basaltic debirs or the magma that rolled or flew into the water basin will enrich the ore-forming elements.That is the machnism in which the metallogenic material of the Qinglong Shazi Sc ore deposit is extracted in quantity from Emeishan basalts by hydrolysis.Thirdly,migration and enrichment process of scandium:According to the study of the Qinglong Shazi Sc deposit,including the mineralogy of basalt,the species of Sc,geochemical characteristics of the major and trace elements,geochemical characteristics of scandium elements,etc,it can be concluded that the content of Sc is high in pyroxene,which is the main dark mineral of Emeishan basalts,and the Sc⁺³ in basalts cannot exist as an independent mineral,but substitute Fe²⁺and Mg²⁺in pyroxene unequivalently.In the Qinglong area in Guizhou,the Maokou group limestone in Permian is afftected by the Emeishan hot mantle plume and the crust uplift,with the exposed surface suffered weathering,denudation and Karst,and thereby the palaeogeomorphology of karst plateau and karst depression formed.Due to the near shore tidal flat,there is water remained in the karst depression.The Emeishan basalt in west Guizhou is rich in sodium and poor in potassium,with 5.33 wt%Na₂O and 0.17 wt%K₂O.The Na-riched feldspar is immersed and collapsed in water in the Karst depression,with K⁺enters the clay minerals while Na+dissolves in water.Thus,special geochemical barriers with weak alkaline water formed.In addition,there is sufficient O₂ in these barriers and the water depression is isolated by the Karst highlands,making these weak alkaline water areas relatively isolated and making these geochemical barriers special.Meanwhile,the Shazi ore deposit is located in the impact zone of the Mile-Shizong fault,which is a local heat source area.And high temperature volcanic materials eruptd from the Emeishan basalt magmatic activity droped down in the Karst depression and formed hydrothermal environment with low temperature.According to the thickness of the pyroclastic sediments in the Karst depression,it infers that the water depth is several tens of meters,supply a certain static pressure.This low temperature and low pressure environment provides essential conditions for the formation of anatase in the studied region.At the early Longtan period in Periman,the Qinglong distinct in Guizhou is on the belt of shore tidal flat facies.The Emeishan mantle plume resulted in crust uplift,accompanied by the strong eruption of the Emeishan basaltic magma.The erupted materials rolled down into the various weak alkaline water bodies with low T-P conditions in the Karst depression.These materials is immersed in water and collapsed.The dark mineral pyroxene dissociated into chlorite,with almost all the Sc⁺³ migrated into the water and formed Sc?OH?₃ or Sc₂O₃ absorbed by the clay minerals,ferric oxide and manganese soil.Thereforoe,a large number of scandium adsorbed mineral bodies such as clay minerals,ferric oxide and manganese soil are formed,which can accept the subsequent deposited matter.Finally,the process of re-enrichment of scandium under the condition of epigenetic condition:In the early of Longtan group of the Late Permian in the special Karst depression in the formation of scandium containing anatase and the mineral,iron oxide,manganese soil adsorbed scandium in a large number of scandium.These scandium deposits suffered the coveration by subsequent stratigraphic material deposition and long geological evolution.After the rapid crustal uplift in the Himalayan period,these scandium ores experienced long-term weathering,leaching and soil formation under Cenozoic supergene conditions.These scandium ore bodies are in the process of soil formation,because the adsorption of scandium is basically not migrated by the adsorption of clay minerals and other active impurities are removed by migration and Further laterite of scandium ore body and surrounding rock.Scandium is kept stable under normal temperature and atmospheric pressure,in situ and near and a large number of active impurities in the scandium ore are leached and scandium is further enriched and re enriched,forming a scandium deposit of the residual slope of Qinglong sand.Through the various aspects of the Inductive analysis,Analysis and demonstration and comprehensive research,the main achievements in this thesis titled with"Study on the genetic process of the Shazi independent scandium deposit in Qinglong County,Guizhou Province"are as follows.1?Qinglong Shazi scandium ore orebody occurs in Middle Permian Maokou limestone Karst unconformity quaternary eluvial slope on the surface of laterite soil,scandium industrial ore produced in three miniaturized depressions 1338.90¹498.45m elevation of Karst hill and in the gentle slope.Three of the identified industrial orebodies are arranged in the south-east to the west,and are numbered in sequence:No.1 scandium ore body,No.2 scandium ore body and No.3 scandium ore body.2?The scandium minerals in Qinglong Shazi are mainly red,yellow clay and subclays.Clay often contains breccias such as siliceous limestone,siliceous rock,iron manganese clayey rock and tuff.The ore minerals are mainly anatase and limonite.Gangue minerals are mainly kaolinite,quartz,sericite?white?mica,chlorite,Plagioclase,zircon and so on.No Independent minerals of scandium be found.The occurrence state of Sc in Qinglong Shazi mine is adsorbed in the form of ions in clay minerals and limonite.It occurs in anatase in the form of isomorphism.3?Through the geochemical characteristics of major elements REE geochemistry,trace element geochemistry,zircon morphology,trace elements,U-Pb ages,Hf isotope and fresh basalt,altered basalt laterite and magnetite in Fe isotopic composition and so on in Qinglong Shazi ore,,can be obtained as follows:?1?Through the REE distribution pattern of mineralized laterite,altered basalt,Pillow Basalt and limestone in Qinglong Shazi scandium mining area shows that the laterite in Qinglong Shazi scandium ore is a product of basalt weathering,and has no genetic connection with the underlying Maokou limestone.?2?The zircon in Qinglong Shazi mine is angular or sub angular,suggesting that zircon has not been transported remotely.Trace element characteristics indicate that it is a basalt magmatic zircon.?3?The zircon U-Pb age of the Qinglong Shazi scandium is 259Ma,which is the same as the main eruption period of the Emeishan igneous province.?4?The Hf isotopic composition of zircon in the Qinglong Shazi scandium is basically the same as that of other basaltic zircon from the other Emeishan igneous province.?5?The metallogenic material of Qinglong Shazi scandium is derived from the basalt of Emeishan,and the formation of the element combination of Sc-TiO₂-Cu-Fe-Mn with high positive correlation level in the ore.?6?The Fe isotopic composition of magnetite can be seen:a).The Fe ion is changed from two valent iron to trivalent iron.It indicates that the laterite of Qinglong Shazi deposit is basaltic parent rock.Under the oxidizing environment,the altered basalt has a lower value of?⁵⁶Fe,and the content of Fe is almost the same as that of fresh basalt,indicating that the whole system is in situ hydrolytic weathering.b).According to the Fe Isotope thermometer,the iron isotope composition of the magnetite in the altered basalt is obtained,and the temperature of the altered fluid is between 70C and 80 C.c).The value of?⁵⁶Fe in scandium red soil decreased significantly,but the iron content increased significantly,indicating that other elements such as Si,Na and Ca lost in hydrolysis weathering process.The migration of easily soluble elements is the main reason for the accumulation of insoluble elements such as Fe,Ti and Sc.?7?From the morphology,age characteristics and Hf isotopes of zircon from mineralized red soil,it is inferred that the Emeishan basalt is its parent rock.The weathering and hydrolysis of basalt may be the main reason for the formation of red soil,and the alteration of basalt is considered as the intermediate product of the weathering of basalt to the laterite.It is inferred that the formation of the red soil in the Qinglong Shazi scandium deposit is related to the hydrolytic weathering of the Emeishan basalt.Under oxidizing conditions,the reaction of basalt with 80°C?or higher temperature?fluid,plagioclase and clinopyroxene are completely decomposed,forming kaolinite,and the Fe²⁺released at the same time is oxidized to Fe³⁺precipitation in situ,forming new iron oxides.Sc and other ore forming elements are released during hydrolysis,and are adsorbed by iron oxides and clay minerals.With the loss of soluble components,they are relatively enriched in the residual phase.4?The scandium of the Qinglong Shazi independent scandium ore deposit can only be formed under the condition of sufficient oxygen supply,low temperature low pressure and weak alkaline environment.Therefore,the formation of scandium must have the following five geological conditions.?1?The source of the basalt is relatively simple:the Emeishan basalt is probably the only parent rock,and it is a source of material for the formation of scandium.?2?The weathering might be thorough:plagioclase,clinopyroxene and ilmenite can hydrolyze,form clay minerals and iron oxides,and redistribute the ore-forming elements.With the loss of soluble elements,the elements which are not soluble easily,such as Fe,Ti and Sc,are relatively enriched.?3?A large number of hot fluids are involved:the Fe isotope composition indicates that the fluid temperature of the metasomatism of the basalt should be at 70-80 C,or even higher.The first is to speed up the thermal fluid mineral weathering and hydrolysis;The second fluid to form anatase;The third can take away a lot of soluble substances,is conducive to the relative enrichment of insoluble elements.?4?Oxidizing environment:indicates that the change of iron isotopic composition and whole rock iron content by clinopyroxene decomposition of Fe²⁺was in situ oxidized to Fe³⁺,and then settled down;and the decomposition of ilmenite into anatase,also need oxidation environment.?5?Low temperature,low pressure and weak alkaline medium oxidize the environment for a long time.In this system,the ore-forming material is in situ weathering and hydrolysis,and does not generate the incoming and discharging of minerals,so that the anatase can exist stably.5?The Qinglong Shazi scandium mine meets 5 geological conditions for the formation of scandium ore.There is a material source of scandium in the scandium mining area in Qinglong Shazi,that is,the scandium of the scandium deposits originates from the basalt of Emeishan.Guizhou Qinglong area in the early Middle Permian Maokou stage is the tidal flat facies Dongwu movement crustal uplift at the same time,with a strong Emeishan basalt eruption,Emeishan basalt eruption volcano flowing into the water will soak into rolled disintegration,dark mineral pyroxene dissociated into chlorite,were isomorphous form scandium and pyroxene Sc³⁺almost all precipitation into the water,provides a rich source for the region formed scandium scandium ore.Guizhou Qinglong area in middle Permian Maokou Formation limestone affected by Emei mantle plume activity of crustal uplift,the top of the exposed surface and occurrence of karst palaeogeomorphology,produced relatively isolated highlands of Karst and Karst depression,the formation of a special geochemical barrier.Due to the tidal flat near the shore,there is water in the part of the Karst depression.The basalt in Qinglong Shazi area is rich in sodium and potassium.The feldspar,rich in sodium,disintegrates and disintegrates in the water of Karst depression.K⁺enters the clay mineral,and Na⁺dissolves in the water,so that there are special geochemical barriers for the weak alkaline water Karst depression.In addition,the karst depression with the weak alkali water in the surface oxidation zone has sufficient oxygen to prepare sufficient conditions for the formation of scandium?TiO₂?.In the metallogenic epoch,the basaltic magma eruption period of Emeishan is a local heat source area.Moreover,Emeishan basalt erupts high temperature volcanic material and falls into the Karst depression to form the surface hot water.According to the thickness of volcaniclastic sediments in Karst depression,the water body at that time is several ten meters deep,and has a certain static pressure,which is suitable for low temperature and low pressure environment to meet the formation conditions of Sc.6?The study of the metallogenic process of the Qinglong sand scandium deposit shows that the whole metallogenic process is divided into two metallogenic stages.The early Longtan"jet"hot water deposition stage in the Late Permian is the main metallogenic period of the deposit.Qinglong Shazi along the Middle Permian Maokou Formation limestone top for tidal flat,there are a number of ancient landform highlands of Karst and Karst water depression.Strong eruption of Emeishan basalt magma in the early Longtan group of the Late Permian,the low eruption of Mount Emei basalt magma in the Qinglong Shazi area flows into the water body to form a basalt rock with little thickness,they are strongly dipped and disintegrated with a few meters deep sea water,because these basalts are not thick in thickness,let basalts get full sea water in the sea,let pyroxene and other mineral dissociation,a large number of Sc³⁺and Ti⁴⁺are released from the top of the ancient Karst water accumulation depression at the top of maomo limestone;Leaching and disintegration of sodium rich feldspar in the water body of Karst depression,Na⁺dissolves in water,the water accumulation in the special Karst depression in the area is weak alkaline water,in this favorable metallogenic environment,the dipped Sc³⁺forms Sc?OH?₃ or Sc₂O₃ colloids or collaterals which are adsorbed by iron oxide,manganese soil and clay minerals to form a"jet"hot water deposited scandium deposit.The Cenozoic era epigenetic weathering-Leaching-soil mineralization stage:Rapid crustal uplift of neotectonic movement in the Himalayan period nudity of Qinglong Shazi scandium ore body and these"jet"hot water deposited scandium deposits are further subjected to long-term weathering-Leaching-soil formation in situ and near the site,through the strong laterite effect made a large number of active impurities are taken away,scandium is preserved by adsorption of clay substance and further rich in scandium ore in soil and formation of scandium deposits with residual slope.The Qinglong Shazi scandium deposit is due to theExhalative hydrothermal sedimentary-residual deluvial deposit,which is related to the eruption of Emeishan basalt.7?Comprehensively observed the geological characteristics,formation process and genetic mechanism of Qinglong Shazi anatase deposit can know that the two deposits are produced not only in the same mining area but also in the same ore bodies;Not only the ore structure and structure are the same,but the ore type is the same;It not only has the same metallogenic geological conditions,but also is formed in the process of the same geological mineralization;The grade and scale of scandium and anatase in the two deposits are both large and independent;Therefore,the Qinglong Shazi scandium deposit and the Qinglong Shazi anatase deposit are not only the symbiotic deposits,but also the two separate ore deposits.8?The activity of the Emei mantle plume and it's lithology is mainly the mafic eruption rock and its associated intrusive rocks.Because of the band a variety of metallogenic elements and their strong volcano power and energy from the mantle,the long cycle of activity,multi cycle,the ore-forming material,the mineralization is complex,therefore to re-examine the western China column Emei mantle heat,especially in the west of Guizhou metallogenic contribution has been some scholars thinking and research direction.Because of the cyclical and polycyclic activities of Emei mantle plume,coupled with the complex palaeogeomorphology and landform in Western Guizhou,the interface between basalt erupted and the ground contact at that time formed different mineral resources.The"Study on the genetic process of the Shazi independent scandium deposit in Qinglong County,Guizhou Province"thesis can further inspire the researchers to seriously examine the contribution and complexity of the basalt in the western part of Guizhou,and explore new ideas for prospecting.It is a great contribution of this doctoral dissertation to indicate the genesis of the ore deposits in the area.