Study On Petro-mineral Features And Genetic Mechanism Of Luodian Jade, Guizhou Province

Luodian Jade, a new members of the nephrites’ family，which is the mostimportant jade in China, was found in Luodian country from Guizhou province in2009,been after preliminary study confirmed that it is a new kind of nephrite on genesis. Inthis paper, not only did the author systematic and deeply study the characteristics ofmineral petrology and geochemical of Luodian Jade in combination with the projectnamed 《the survey evaluation of nephrite ore region in Luodian-Wangmo fromGuizhou》, but preliminary discussed the genetic mechanism and proposed aclassification and quality evaluation criteria of Luodian Jade as well.The ore or mineralization points of Luodian Jade are mainly dispersed through outcontact with metamorphic zone on diabase body. The ore was classified as calcitemarble, diopside^tremolite marble, siliceous （quartz） marble^siliceous rock zone（quartz） and tremolite jade belt combined with the field and indoor study, and in whichtremolite jade （jade） band is a main mineralization belt of Luodian Jade and presentscharacteristics by many metasomatic metamorphism. The mainly alteration typesinclude marmorization, tremolitization and kaolinization, in which, marbleizationgenerally only take place on diabase underlying rock but, tremolitization andkaolinization are restricted to overlying rock. Usually, the shape of alteration zone islong lenticular and cystic body occasionally, and that outside contact of alteration zonehas also diopsidization, wollastonitization and steatitization besides marbleization andtremolitization. Ore body occurred mainly as marmorization limestone, whichcontaining tremolite marble, quartz-calcite marble, quartzite and tremolite-wollastonitequartzite, etc.Mineral composition of Luodian Jade priority is tremolite, which content in commonly is more than95%and contains a small amount of diopside, calcite, quartz,etc. Microstructure of jade mainly is blastic texture including several kinds ofmicrostructure characteristics such as fiber-needle, porphyroblast metacryst pilotaxitictexture, blanket crystalloblastic metacryst pilotaxitic texture, flake crystalloblasticmetacryst pilotaxitic texture, fibrous crystalloblastic metacryst pilotaxitic texture andgranular metacryst pilotaxitic texture and so on, and there are some kinds of structurecharacteristics of jade such as dense block, veinlet belt, brecciated structure,replacement of residual tectonic etc. Replacement texture mainly metasomatismresidual structure, including residual island metasomatism, net vein metasomatism,vein metasomatism, alteration-pseudomorphism and corrode.Petrochemical characteristics of Luodian Jade from Guizhou Province werestudied by XRF, ICP-MS and conventional chemical analysis. Tremolite in LuodianJade experienced two stages of relative saturated and unsaturated in Mg.Analysis of trace element shows that the formation of white jade series and greenjade series is affected by different trace element associations, especially, Cr-V, Co-Niand Mn-Sr. It is indicated that Cr and V ions in chemical composition are responsiblefor the green color of Luodian Jade. Moreover, REE analysis of Luodian Jade revealedt abnormal characteristics in δCe and δEu, and chondrite-normalized REE distributionpattern is similar to that of the surrounding rock of diabase and limestone. Analysis ofsilicon and oxygen isotope and results ofδ¹⁸O fractionating equation calculation in theore-forming fluid show that Luodian Jade belongs to the low temperature liquid deposit.On the basis of petro-chemical characteristics study of Luodian Jade, it is consideredthat Luodian Jade is a new type of nephrite jade formed in a long-term contactmetasomatism between the limestone and gas-liquid fluid brought by diabase intrusive.In the process of metallogenic metasomatism, the limestone provides Ca and Mg, andthe gas-liquid fluid mainly provides Si for Luodian Jade. Because each stage ofhydrothermal activity, physico-chemical conditions and geological processes wasdifferent then the mineralization of Luodian Jade has multiple stages, so that it formingore body of Luodian Jade has different structure characteristic and jade’s performance.Test of basic physical and optical properties in Luodian Jade show that jade’s coloris given priority to with white, bluish white, green color and named "spotted jade"because of iron and manganese disseminated. Luster of jade from deposits general isporcelain, waxy and weak oily, and which from natural fracture or artificial cut surfaceis more than waxy and oily. The refractive index, Vickers-hardness, mohs hardness anddensity of Luodian Jade are similar to other neiphrite, and it is different from other types of nephrite that luminescence on UV, which feature is send out green fluorescencein the long wave UV and short-wave UV with brownish tone in the yellow-greenfluorescence, moreover, also has different intensity on the cathode luminescence.Results of SEM showed that the quality of jade is association with granularstructure and close degree of tremolite in Luodian Jade. XRD test confirmed that thecrystallinity of Luodian Jade is higher than other nephrite from Xinjiang, Qinghai,which crystal structure has a little difference with standard tremolite, and HT-XRDexperiment confirmed the mechanism of diopside formation in tremolite+calcite+quartz coexistence system; EPR show that the EPR of Fe³⁺and Mn²⁺in Luodian Jaderesonance spectra are very similar, the Mn²⁺ion resonance absorption to isotroPhoto, itscoordination polyhedra are nearly cubic symmetry of the structure environment, Fe³⁺ions in the vicinity of160mT to resonance spectrum nearly isotroPhoto, its symmetry ishigher, in which there is a widespread isomorphism replacement with Mn²⁺to Mg²⁺ionin the position of octahedral. Weak but very clear shoulder shape absorption band at840cm-1⁸60cm-1was appear on the most of the samples of IR test in Luodian Jade,which within the frequency band of absorption is unique to Luodian Jade but didn’tappear on natural neiphrite, that is caused by residue diopside in the process offormation jade. By using the result of EMPA and IR tests provide the fine structurefeatures, the crystals chemical formula of tremolite in Luodian Jade had beencalculated.On the one hand, the color of Luodian Jade is caused by the absorption in thevisible area, mainly by Fe²⁺â†'Ti⁴⁺charge transfer spectrum （at490nm⁵00nm）,⁶A₁â†'⁴T₂（⁴G） of Fe³⁺electron transition （at615nm⁶32nm,685nm⁶94nm） and⁴T₁（⁴G）â†'⁶A₁（⁶S） of Mn²⁺electron transition （549nm⁵60nm）, on the other hand alsoinvolves some impurity ions in the composition of jade, content and form, and therelative content of impurity ions, which is the integrated result of various factors; Thetest of Luodian Jade absorbance show that the transparency has a close relationship tocomposition and distribution of the mineral in Luodian Jade. Different crystals grainsize and mineral distribution of tremolite of different structures, its sensorytransparency also is different. Otherwise, impregnation degree of iron and manganese,fracture, location, etc., are the factors lead to the change of the sensory transparency;High toughness of Luodian Jade was studied basing on the principle of Griffith cracktheory and combinating the results of scanning electron microscopy （SEM）, it wasconsided as related to its internal grain interface, the cleavage plane and the size of themicro cracks and pore and its development. In this paper, it was put forward that the classification and naming scheme ofLuodian Jade, which the color was mainly consided as the main classification basis; Inquality grading of Luodian Jade which was mainly consided that including factors suchas structure, transparency, clarity etc, could be divided into four levels from Optimal toâ…¢, the comprehensive quality ofLuodian Jade could be divided into three levels on thepremise that comprehensive consider color, texture and clarity as well as.By preliminary comparative researching with nephrite of other regions and theproperties of curing of Luodian Jade, however, except a few most of Luodian Jade itwas thought that there is a certain gap comparison with others high quality neiphritefrom Xinjiang, Qinghai and other places on the oiliness, which impacted the productsquality of Luodian Jade’s visual of; In addition, the defect was also another factor toinfluence the curing performance of Luodian Jade. Market value of Luodian Jade willbe likely to increased only around these two aspects in the machining process and to besolved by certain technical.The innovation of this study is mainly reflected in the following aspects:（1）Systematically analysised the petrological, mineralogical and geochemicalcharacteristics of Luodian Jade using testing technology of traditional combinationwith modern. For the first time, to obtained the characteristic absorption spectrum ofdiopside in natural nephrite samples by IR testing, and more deeply to study themechanism of color, influence factors of luster and transparency by using microscopephotometer, SEM and XRD; Further, preliminary to discussion on the formingmechanism of diopside in Luodian Jade using high temperature in situ XRD method.（2）High toughness of Luodian Jade was studied basing on the principle ofGriffith crack theory and combinating the results of SEM for the first time, it wasconsided as related to its internal grain interface, the cleavage plane and the size of themicro cracks and pore and its development.（3）Confirmed that Luodian Jade is a kind of new genetic types. Comprehensiveanalysed suggest that the ore-forming mechanism of Luodian Jade is concluded andregarded that as the contact metamorphism between basite and carbonatite according todeposit geological characteristics, metallogenic material source and fluid properties, etc.Because each stage of hydrothermal activity, physico-chemical conditions andgeological processes was different then the mineralization of Luodian Jade has multiplestages, so that it forming ore of Luodian Jade has different structure characteristic andjade’s performance.（4）According to Luodian Jade’s own specialties to put forward the scheme of classification and naming to focus on color as the main factor; Comprehensivelyevaluated from some factors including color, texture, purity, cure and size combine withlaboratory analysis and appraisal, simultaneously, according to Luodian Jade’s marketconditions, for the first time, Luodian Jade’s classification is put forward to be dividedinto Optimal^â…¢ four levels and the quality is divided into three grades.