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The Mineralogical Characteristics Of Albitite From Myanmar Jadeitite Deposit

Posted on:2015-03-20Degree:DoctorType:Dissertation
Country:ChinaCandidate:J WangFull Text:PDF
GTID:1260330428474734Subject:Mineralogy, petrology, ore deposits
Abstract/Summary:PDF Full Text Request
Albitite, a type of rock composed principally of albite, is rare to find.Albitite isfound in several geolocal settings, one of which is in assocation with jadeitite, a rockmade up almost entirely of jadeitic pyroxene and forms under a relatively high-P/Tcondition in the subduction zones. Jadeitites have attracted much attention fromgeologists and gemologists internationally, and many sites of jadeitites have been welldocumented. However, there has been little understanding about the albitites, whichare always associated with jadeitites. The Myanmar jadeite deposit, where someclassic mineral relationships are preserved, is also home to the best samples ofalbitite.Albitite is mainly composed of low-temperature albite, pyroxene minerals such asjadeite, omphacite and dioside and amphibole minerals such as richterite, winchiteand magnesio-riebeckite, natrolite, pectolite, Ba and Sr minerals. Replacement of thejadeite by albite in the albitite along its cleavage and crack indicates that albite formslater than the jadeite. Diopside in the albitite consists of two types: one formed byreplacement of jadeite which contains some components of dioside, the other isinferred to be the residual which was part of the replaced rocks like rodingite orpyroxenite belonging the host serpentine mélange. The latter can be used asmineralogical evidence for confirmation of jadeitized pyroxenite and jadeitizedrondingite.Replacement of the jadeite by albite indicates the metasomatic origin of albitite.However, we can not exclude the origin of vein crystallization from fluids in thesamples that do not have replacement texture. Micro-Raman spectroscopy,QMS(Quadrupole mass spectrometry) and ion chromatograph were used to detectcomponents in the fluid inclusions, obtain information about additional volatiles andmeasure the bulk cation and anion contents of the fluid inclusions. The fluidinclusions in the albitites are mainly composed of H2O,QMS measurements haveshown that the bulk fluids contain93.01-98.37mol.%H2O. The samples arecharacterized by ionic contents higher than that of in the jadeitites, the most abundantcation being Na+, Ca2+and Mg2+and the most abundant anion are F﹣and Cl﹣.Combined with the Ba and Sr minerals in the albitites, it can be speculated that the albitite-forming fluids might be derived from the residual fluids of the jadeitites.Existence of the albite shows that Na-rich fluids are thorugh and traversing.Similar to jadeitite, albitite from Myanmar can be classified into two types:undeformed albitite and deformed albitite. The deformed textures include crystallineorientation, mechanical twin, sub-grain, serrated high-angle sutured grain boundariesand recovery textures. Transformation of coarse albitite into the transparentgem-quality albite jade, should have undergone at least two coupled processes ofgrain size reduction and crystallographic orientation. The main processes causingthese are progressive misorientaion of sub-grains and grain-boundary migration. Theexistence of these deformation textures indicate that the most transparent albite jadehas undergone long-lasting and intensive, localized geological forces. It is very likelythat the source of these forces is linked to the major Sagaing stike-slip faults.
Keywords/Search Tags:Myanmar, albitite, jadeitite, subduction zone, Na-rich fluid
PDF Full Text Request
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