辽宁瓦房店金伯利岩中石榴石特征及种类鉴定

辽宁瓦房店金刚石矿区金伯利岩中的石榴石一直被当作镁铝榴石。为了确定矿区颜色复杂的石榴石种类,本文对矿区的石榴石进行了系统的采样分析,测定了112件石榴石样品的晶胞参数、50件样品的微区化学成分和40件样品的红外光谱。利用石榴石晶胞参数、红外光谱、化学成分和化学分子式方法对矿区石榴石进行分类,结果显示:晶胞参数分类法误差大,容易得出错误结论;红外图谱分类法准确度不高,只能作为参考方法;化学成分分类法太过笼统,达不到详细划分石榴石种类的目的;化学分子式分类法可把矿区的石榴石详细划分6个矿种:镁钙铁-铝铬铁榴石、镁铁钙-铝铬铁榴石、镁钙铁-铝铬榴石、镁钙-铝铬铁镁榴石、镁铁钙-铝铬榴石、镁铁钙-铝铁铬榴石,每种石榴石都充分反映了A、B离子的种类及占位特征,是4种分类方法中最为科学的方法。研究认为瓦房店金刚石矿区金伯利岩中石榴石A端元成分以Mg²⁺离子占位为主;B端元成分以Al³⁺离子占位为主。由于阳离子替代普遍,A、B端元成分复杂,瓦房店金伯利岩中不存在单纯意义上的镁铝榴石。     

镁铝榴石成分特征的统计分析与金伯利岩含矿性

镁铝榴石是金伯利岩中最重要的标型矿物,在金刚石矿床普查中具有重大意义.文中利用了钛分异系数,对镁铝榴石氧化物成分作了对应分析.同时按其颜色成分作了聚类分析,划分了各种石榴石成分及镁铝榴石颜色系列.研究了镁铝榴石结晶机制及岩浆分异作用,结合金伯利岩的判别分析及地质构造特征的分析,作出了镇远施秉金伯利岩群含矿性很差,远景不大的结论.     

我国金伯利岩中镁铝榴石的化学成分特征及找矿意义

镁铝榴石是金刚石的重要伴生矿物,而在许多非金伯利岩中也含有镁铝榴石,因此深入研究金伯利岩中与非金伯利岩中镁铝榴石的物理、化学特征,找出它们之间的差异进而确立金伯利岩中镁铝榴石的标型特征,对利用重砂法寻找金刚石原生矿具有重要意义。本文仅对我国已发现的金伯利岩中镁铝榴石的化学成分特征及与非金伯利岩中镁铝     

金伯利岩中镁铝榴石端员分子计算方法的探讨

镁铝榴石是金伯利岩的重要副矿物之一。根据岩石学、热力学和地球物理学的研究,它与金刚石都属于深成高温高压标型矿物。镁铝榴石具有较稳定的物理化学性质,因此,在后期地质作用(蚀变或风化搬运)过程中,能较好地保存下来。而且金伯利岩中的镁铝榴石,因含有较多的铬与镁,颜色较特殊,在重砂或手标本中容易鉴定。     

我国金伯利岩及其他岩类中的镁铝榴石

镁铝榴石是金伯利岩的副矿物,也常产于橄榄岩、榴辉岩、偏碱性玄武岩、超基性煌斑岩中。因此,确定金伯利岩中镁铝榴石的标型特征,是金刚石找矿和评价工作中的一个重要课题。 本文研究了我国常马庄、头道沟、马坪、彭家榜、土门等地区金伯利岩中镁铝榴石的物理性质和化学特征,并与其他岩类中的镁铝榴石作了对比,探讨了镁铝榴石的标型特征及其与含矿性的关系。     

湖南桃源理公港地区含金刚石沉凝灰岩的发现及其找矿意义

湖南桃源理公港地区白垩纪红盆内的灰绿色和紫红色沉积夹层曾选获过金刚石。以灰绿色岩石为研究对象,通过薄片鉴定和电子探针分析来确定岩石名称和岩石中石榴石和云母的属性。显微镜下,灰绿色岩石呈凝灰结构,由约45%的晶屑、35%的岩屑和20%的玻屑组成,为较典型的沉凝灰岩,并非前人所述的金伯利岩。沉凝灰岩中的石榴石和云母分别为G10型镁铝榴石和金云母,镁铝榴石和金云母的成分与辽宁、山东及南非典型岩管含金刚石金伯利岩中的镁铝榴石及金云母的成分基本一致,暗示其来源于含金刚石的金伯利岩。沉凝灰岩的特征表明,其来源地不会太远,这为在附近找寻火山机构奠定了基础; 金伯利质岩屑、G10型镁铝榴石和金云母的发现,为在周边寻找原生金伯利岩提供了重要信息。     

湖南桃源理公港地区含金刚石沉凝灰岩的发现及其找矿意义

湖南桃源理公港地区白垩纪红盆内的灰绿色和紫红色沉积夹层曾选获过金刚石。以灰绿色岩石为研究对象,通过薄片鉴定和电子探针分析来确定岩石名称和岩石中石榴石和云母的属性。显微镜下,灰绿色岩石呈凝灰结构,由约45%的晶屑、35%的岩屑和20%的玻屑组成,为较典型的沉凝灰岩,并非前人所述的金伯利岩。沉凝灰岩中的石榴石和云母分别为G10型镁铝榴石和金云母,镁铝榴石和金云母的成分与辽宁、山东及南非典型岩管含金刚石金伯利岩中的镁铝榴石及金云母的成分基本一致,暗示其来源于含金刚石的金伯利岩。沉凝灰岩的特征表明,其来源地不会太远,这为在附近找寻火山机构奠定了基础;金伯利质岩屑、G10型镁铝榴石和金云母的发现,为在周边寻找原生金伯利岩提供了重要信息。     

湖南桃源理公港地区含金刚石沉凝灰岩的发现及其找矿意义

湖南桃源理公港地区白垩纪红盆内的灰绿色和紫红色沉积夹层曾选获过金刚石。以灰绿色岩石为研究对象,通过薄片鉴定和电子探针分析来确定岩石名称和岩石中石榴石和云母的属性。显微镜下,灰绿色岩石呈凝灰结构,由约45%的晶屑、35%的岩屑和20%的玻屑组成,为较典型的沉凝灰岩,并非前人所述的金伯利岩。沉凝灰岩中的石榴石和云母分别为G10型镁铝榴石和金云母,镁铝榴石和金云母的成分与辽宁、山东及南非典型岩管含金刚石金伯利岩中的镁铝榴石及金云母的成分基本一致,暗示其来源于含金刚石的金伯利岩。沉凝灰岩的特征表明,其来源地不会太远,这为在附近找寻火山机构奠定了基础; 金伯利质岩屑、G10型镁铝榴石和金云母的发现,为在周边寻找原生金伯利岩提供了重要信息。     

河南鹤壁地区金伯利岩中地幔包体矿物化学特征

河南鹤壁地区位于太行山构造带上,该区金伯利岩中的地幔包体携带有岩石圈地幔的丰富信息。本文报道了石榴石二辉橄榄岩包体中的镁橄榄石和镁铝榴石的矿物化学特征。金伯利岩中地幔包体的镁橄榄石I(Mg~#)为91.7±0.2(n=69)。与鹤壁地区尖晶石相方辉橄榄岩相比,I(Mg~#)略偏小,指示二辉橄榄岩经历的熔融程度较低,具有过渡型地幔的特征。根据Cr_2O_3含量,镁铝榴石可以划分为高铬系列和低铬系列两类。橄榄石-石榴石矿物温压计计算表明,包体压力在1.7~2.5 GPa之间(55~80 km),温度在641~1055℃之间,对应的大地热流值为50~60m W/m~2,甚至更高。指示金伯利岩侵位时对应于较高的大地热流条件。根据Grutter的镁铝榴石划分方案,镁铝榴石主要划分为G9型、G3和G4型,其中G3和G4型镁铝榴石记录了岩石圈地幔被交代的过程。根据温压条件及岩石圈地幔性质,可以认为鹤壁地区不具有形成金刚石矿的深部地质条件。     

辽宁金伯利岩中镁铝榴石与金刚石的关系

辽宁金伯利岩中镁铝榴石的含量与金刚石的含量成正比。富含矿的岩体中镁铝榴石颜色有紫色、红色和橙色等种类,其中以紫色的为主,金刚石的含量越多紫色类型所占比例就越大。 镁铝榴石中Cr_2O_3和CaO的含量随其颜色的加深而升高;Al_2O_3、MgO、TiO_2的含量变化则相反。富矿岩体中富铬(>5％)镁铝榴石的含量高于中等含矿和贫含矿的岩体。 文中还列出了山东和贵州金刚石矿中镁铝榴石的资料以资对比。     

Mineralogical studies of pyropes in kimberlites from China

Based on the measurements of refractive index,specific gravity,unit cell parameter,and mineral chemistry and infrared absorption spectrum analyses of pyropes in kimberlites from China,systematic studies of the Physical properties and compositional variations of pyropes of different colors and diverse paragenetic types,within and between kimberlite provinces have been undertaken,The origin of pyropes in the Kimberlites and the depth of their formation have been discussed.Pyropes of the purple series are different from those of the orange series in physical and chemical properties,for exaple,pyropes of the puple series are higher in α0,RI,SG,Cr2O3,MgO,Cr/(Cr Al),Mg/(Mg Fe),and Mg/(Mg Ca),and lower in Al2O3,Fe2O3 FeO than those of the orange series.The classification of garnets in kimberlites from china by the Dawson and Stephens‘ method(1975) has been undertaken and clearly demonstrates that pyropes of diamond-rich kimberlites contain much more groups than those of diamond-poor,especially diamond-free kimberlites.The higher in α0,RI,SG,Cr2O(3.Cr/(Cr Al),knorringite and Cr-component the pyropes are ,the richer in diamond the kimberlites will be.The infrared absorption spectrum patterns of pyropes change with their chemical composition regularly,as reflected in the shape and position of infrared absorption peaks.Two absortpion bands at 862-901 cm^-1 will grade into degeneration from splitting and the absorption band positions of pyropes shift toward lower frequency with increasing Cr2O3 content and Cr/(Cr Al) ratio of pyropes,LREE contents of orange pyrope megacrysts are similar to those of porple pyrope macrocrysts,but the former is higher in HREE than the latter,showing their different chondrite-normalized patterns.The formation pressures of pyropes calculated by Cr-component,Ca-component,knorringite molecules of pyropes show that some pyropes of the purple series in diamondiferous kimberlites fall into the diamond stability field.but all pyropes of diamond-free kimberlites lie outside the diamond stability field.The megacrysts were formed through early crystallization of kimberlites magma at high pressure condition,the majority of the purple pyrope macrocrysts have been derived from disaggregated xenoliths but the minoirty of them appear to be fragments of the discrete megacryst pyropes,or phenocrysts.     

中国金伯利岩中的钛铁矿

本文研究了金伯利岩中,作为巨晶和粗晶,基质相矿物,与金云母、镁铝榴石、铬尖晶石等矿物的连生体,金刚石中包裹体矿物及金伯利岩地幔岩包裹体矿物产出的钛铁矿的大小,形态、皮壳及化学成分、端元组分、环带及成分变异趋势。并与其他岩类中的钛铁矿作了对比。探讨了不同产状、共生组合类型的钛铁矿的成因。指出了与金刚石紧密伴生的钛铁矿的标型特征及找矿意义。     

Systematic variations in xenocryst mineral composition at the province scale, Buffalo Hills kimberlites, Alberta, Canada

The Buffalo Hills kimberlites define a province of kimberlite magmatism occurring within and adjacent to Proterozoic crystalline basement termed the Buffalo Head Terrane in north-central Alberta, Canada. The kimberlites are distinguished by a diverse xenocryst suite and most contain some quantity of diamond. The xenocryst assemblage in the province is atypical for diamondiferous kimberlite, including an overall paucity of mantle indicator minerals and the near-absence of compositionally subcalcic peridotitic garnet (G10). The most diamond-rich bodies are distinguished by the presence of slightly subcalcic, chromium-rich garnet and the general absence of picroilmenite, with the majority forming a small cluster in the northwestern part of the province. Barren and near-barren pipes tend to occur to the south, with increasing proximity to the basement structure known as the Peace River Arch. Niobian picroilmenite, compositionally restricted low-to moderate-Cr peridotitic garnet, and megacrystal titanian pyrope occur in kimberlites closest to the arch. Major element data for clinopyroxene and trace element data for garnet from diamond-rich and diamond-poor kimberlites suggests that metasomatism of lithospheric peridotite within the diamond stability field may have caused destruction of diamond, and diamond source rocks proximal to the arch were the most affected.     

镁铝榴石的化学成分分类及其在金刚石找矿中的指示意义

镁铝榴石是找寻金刚石的一种重要的指示矿物。本文应用了聚类分析方法，以镁铝榴石中的钙组分、铬组分、镁组分和镁组分（铁铝榴石）4种成分参数作变量，将56个样品分为6类，讨论了每一类样品的化学成分特点，确定了它们的标型意义，并应用多元判别分析得出了划分这6类和对未知样品进行判别归类的一组判别函数。     

The Fazenda Largo off-craton kimberlites of Piauí State, Brazil

In the late 1990s, the Fazenda Largo kimberlite cluster was discovered in the Piauí State of Brazil. As with earlier known kimberlites in this area – Redondão, Santa Filomena-Bom Jesus (Gilbues) and Picos – this cluster is located within the Palaeozoic Parnaiba Sedimentary Basin that separates the São Francisco and the Amazonian Precambrian cratons. Locations of kimberlites are controlled by the ‘Transbrasiliano Lineament’. The Fazenda Largo kimberlites are intensely weathered, almost completely altered rocks with a fine-grained clastic structure, and contain variable amounts of terrigene admixture (quartz sand). These rocks represent near-surface volcano-sedimentary deposits of the crater parts of kimberlite pipes. By petrographic, mineralogical and chemical features, the Fazenda Largo kimberlites are similar to average kimberlite. The composition of the deep-seated material in the Fazenda Largo kimberlites is quite diverse: among mantle microxenoliths are amphibolitised pyrope peridotites, garnetised spinel peridotites, ilmenite peridotites, chromian spinel + chromian diopside + pyrope intergrowths, and large xenoliths of pyrope dunite. High-pressure minerals are predominantly of the ultramafic suite, Cr-association minerals (purplish-red and violet pyrope, chromian spinel, chromian diopside, Cr-pargasite and orthopyroxene). The Ti-association minerals of the ultramafic suite (picroilmenite and orange pyrope), as well as rare grains of orange pyrope-almandine of the eclogite association, are subordinate. Kimberlites from all four pipes contain rare grains of G10 pyrope of the diamond association, but chromian spinel of the diamond association was not encountered. By their tectonic position, by geochemical characteristics, and by the composition of kimberlite indicator minerals, the Fazenda Largo kimberlites, like the others of such type, are unlikely to be economic.     

Neoproterozoic ‘anomalous’ kimberlites of Guaniamo, Venezuela: Mica kimberlites of ‘isotopic transitional’ type

In Venezuela, kimberlites have so far only been found in the Guaniamo region, where they occur as high diamond grade sheets in massive to steeply foliated Paleoproterozoic granitoid rocks. The emplacement age of the Guaniamo kimberlites is 712±6 Ma, i.e., Neoproterozoic. The Guaniamo kimberlites contain a high abundance of mantle minerals, with greater than 30% olivine macrocrysts. The principal kimberlite indicator minerals found are pyrope garnet and chromian spinel, with the overwhelming majority of the garnets being of the peridotite association. Chrome-diopside is rare, and picroilmenite is uncommon. Chemically, the Guaniamo kimberlites are characterized by high MgO contents, with low Al₂O₃ and TiO₂ contents and higher than average FeO and K₂O contents. These rocks have above average Ni, Cr, Co, Th, Nb, Ta, Sr and LREE concentrations and very low P, Y and, particularly, Zr and Hf contents. The Nb/Zr ratio is very distinctive and is similar to that of the Aries, Australia kimberlite. The Guaniamo kimberlites are similar in petrography, mineralogy and mantle mineral content to ilmenite-free Group 2 mica kimberlites of South Africa. The Nd-Sr isotopic characteristics of Guaniamo kimberlites are distinct from both kimberlite Group 1 and Group 2, being more similar to transitional type kimberlites, and in particular to diamondiferous kimberlites of the Arkhangelsk Diamond Province, Russia. The Guaniamo kimberlites form part of a compositional spectrum between other standard kimberlite reference groups. They formed from metasomatised subcontinental lithospheric mantle and it is likely that subduction of oceanic crust was the source of this metasomatised material, and also of the eclogitic component, which is dominant in Guaniamo diamonds.     

Distribution of trace elements between garnet megacrysts and host volcanic liquids of kimberlitic to rhyolitic composition

Abundances of rare earth elements, Hf, Sc, Co, Cr and Th in garnet megacrysts and their volcanic hosts or matrices are used to estimate garnet/liquid partition coefficients for these elements. Samples include pyropes from kimberlite and highly alkalic basalts, almandines from basalt andesite, dacite, rhyodacite and rhyolite and a spessartine-almandine from alaskite. The pyrope/host partition coefficients are fairly uniform and agree with experimental data within a factor of 2. The almandine/matrix data show more scatter (due in part to impurities in the garnet separates) but the partition coefficients tend to increase with increasing $\text{Si}\text{O}$ ratio of the matrix. The almandine/matrix partition coefficients are up to a factor of 10 higher than the pyrope/host partition coefficients. The spessartine-almandine is strongly enriched in heavy rare earths (~ 5000 times chondrites), Y, Sc and Co. The wide variation in garnet/liquid partition coefficients from kimberlites to rhyolites cannot be explained as an effect of temperature and we conclude that a major factor is the composition of the melt from which the garnet crystallized.     

大洪山区钾镁煌斑岩的矿物特征及含矿性探讨

本文分析了大洪山区钾镁煌班岩中的矿物特征,利用造岩矿物和副矿物的电子探针分析结果与西溴含金刚石钾镁煌斑岩中相应矿物进行对比。并用特征副矿物镁铝榴石、铬铁矿的化学成分作Cr_2O_3—CaO图,Cr_2O_3-MgO图,利用Cr/(Cr+Al)的比值参数,判别岩体的含矿性。认为该区钾镁煌斑岩目前虽然尚未发现金刚石,但成矿有利因素较多。