全球铬铁矿床成因类型、地质特征及时空分布规律初探     

赵宏军  陈玉明  陈秀法  张潮  何学洲  张福祥  于永善 《矿床地质》2021,40(6):1312-1337

全球铬铁矿资源丰富,但分布极不均衡.铬铁矿的成因类型主要有层状和豆荚状2种,这2种类型的铬铁矿床地质特征、成因模式差异显著.在全球范围内铬铁矿矿床的成矿时代和空间分布具有明显的时空规律性,古元古代是铬铁矿最重要成矿期,该期形成的铬铁矿占总资源量的58.5％,以形成大型-超大型层状铬铁矿为主,中-新生代是全球铬铁矿床形成数量最多、分布范围最广的重要成矿期,该期形成的铬铁矿占总资源量的24.9％,以形成中小型豆荚状铬铁矿为主.铬铁矿在全球的分布可划分为5个重要层状铬铁矿矿田(南非布什维尔德-津巴布韦大岩墙、北美斯蒂尔沃特、南美坎坡福莫索、印度苏金达、芬兰凯米-俄罗斯普拉科夫斯科)和7个豆荚状铬铁矿带(津巴布韦舒鲁圭、东北非、乌拉尔、特提斯、西太平洋岛弧、加勒比岛弧和马达加斯加),并对各重要成矿区带的资源潜力进行了探讨.通过对全球铬铁矿成因类型、地质特征和时空分布规律的探讨,对深入了解地幔的物质组成、物理化学环境、地幔物质的运移、深部地质作用及板块运动的动力学机制、深俯冲和地球深部再循环轨迹有重要的理论意义.  相似文献   

山东蒙阴金伯利岩中铬铁矿电子探针波谱分析     

迟惠中  王大千  李经国  伍月  栗春玲  张媛媛  刘锦岫  肇美晶 《地质与资源》2021,30(2):214-218

铬铁矿是金伯利岩型金刚石矿床中主要的指示性矿物之一.准确分析出铬铁矿化学组分中FeO、MgO、Cr₂O₃、Al₂O₃、TiO₂含量,不但对铬铁矿定名起决定性作用,对金伯利岩型金刚石矿床找矿也具有重要的指示意义.利用电子探针波谱技术对铬铁矿主量化学元素分析,通过所测样品微区化学成分含量推测矿物名称.25件单矿物样品微区化学成分分析结果统计显示：单矿物中主要化学成分FeO为15.666%~29.971%,MgO为7.286%~11.477%,Cr₂O₃为56.421%~71.111%;次要化学成分MnO为0.012%~0.382%,Al₂O₃为0.871%~8.993%,TiO₂为0.074%~3.375%.矿物化学成分总量为99.117%~100.877%,单矿物化学成分与铬铁矿化学组分相当.根据矿物人工重砂鉴定特征及A、B离子占位情况,可以确定所测样品为镁铬铁矿.  相似文献   

Cr-Saturation Arrays in Concentrate Garnet Compositions from Kimberlite and their Use in Mantle Barometry   总被引：2，自引：0，他引：2  

GRUTTER  HERMAN; LATTI  DEWETIA; MENZIES  ANDREW 《Journal of Petrology》2006,47(4):801-820

The spinel–garnet transition in Cr/Al-enriched peridotiticbulk compositions is known from experimental investigationsto occur at 20–70 kbar, within the pressure range sampledby kimberlites. We show that the Cr₂O₃–CaO compositionsof concentrate garnets from kimberlite have maximum Cr/Ca arrayscharacterized by Cr₂O₃/CaO 0·96–0·81, andinterpret the arrays as primary evidence of chromite–garnetcoexistence in Cr-rich harzburgitic or lherzolitic bulk compositionsderived from depth within the lithosphere. Under Cr-saturatedconditions on a known geotherm, each Cr/Ca array implicitlydelineates an isobar inside a garnet Cr₂O₃–CaO diagram.This simplification invites a graphical approach to calibratean empirical Cr/Ca-in-pyrope barometer. Carbonaceous chromite–garnetharzburgite xenoliths from the Roberts Victor kimberlite tightlybracket a graphite–diamond constraint (GDC) located atCr₂O₃ = 0·94CaO + 5·0 (wt %), representing a pivotalcalibration corresponding to 43 kbar on a 38 mW/m² conductivegeotherm. Additional calibration points are established at 14,17·4 and 59·1 kbar by judiciously projecting garnetcompositions from simple-system experiments onto the same geotherm.The garnet Cr/Ca barometer is then simply formulated as follows(in wt %):

if Cr₂O₃ 0·94CaO + 5, then P₃₈ (kbar) = 26·9+ 3·22Cr₂O₃ – 3·03CaO, or

if Cr₂O₃ <0·94CaO + 5, then P₃₈ (kbar) = 9·2+ 36[(Cr₂O₃+ 1·6)/(CaO + 7·02)].

A small correction to P₃₈ values, applicable for 35–48mW/m² conductive geotherms, is derived empirically by requiringconventional thermobarometry results and garnet concentratecompositions to be consistent with the presence of diamondsin the Kyle Lake kimberlite and their absence in the Zero kimberlite.We discuss application of the P₃₈ barometer to estimate (1)real pressures in the special case where chromite–garnetcoexistence is known, (2) minimum pressures in the general casewhere Cr saturation is unknown, and (3) the maximum depth ofdepleted lithospheres, particularly those underlying Archaeancratons. A comparison with the P_Cr barometer of Ryan et al.(1996, Journal of Geophysical Research 101, 5611–5625)shows agreement with P₃₈ at 55 ± 2 kbar, and 6–12%higher P_Cr values at lower P₃₈. Because the P_Cr formulationsystematically overestimates the 43 kbar value of the GDC by2–6 kbar, we conclude that the empirical Cr/Ca-in-garnetbarometer is preferred for all situations where conductive geothermsintersect the graphite–diamond equilibrium. KEY WORDS: Cr-pyrope; chromite; P₃₈ barometer; mantle petrology; lithosphere thickness  相似文献   

Platinum-group Mineral (PGM) and Base-metal Sulphide (BMS) Inclusions in Chromitites of the Zedang Ophiolite, Southern Tibet, China and their Petrogenetic Significance   总被引：1，自引：0，他引：1  

GUO Guolin  YANG Jingsui  Paul T. ROBINSON  LIU Xiaodong  XU Xiangzhen  XIONG Fahui 《《地质学报》英文版》2016,90(3):900-912

Voluminous platinum-group mineral(PGM) inclusions including erlichmanite(Os,Ru)S_2, laurite(Ru,Os)S_2, and irarsite(Ir,Os,Ru,Rh)As S, as well as native osmium Os(Ir) and inclusions of base metal sulphides(BMS), including millerite(NiS), heazlewoodite(Ni_3S_2), covellite(CuS) and digenite(Cu_3S_2), accompanied by native iron, have been identified in chromitites of the Zedang ophiolite, Tibet. The PGMs occur as both inclusions in magnesiochromite grains and as small interstitial granules between them; most are less than 10 μm in size and vary in shape from euhedral to anhedral. They occur either as single or composite(biphase or polyphase) grains composed solely of PGM, or PGM associated with silicate grains. Os-, Ir-, and Ru-rich PGMs are the common species and Pt-, Pd-, and Rh-rich varieties have not been identified. Sulfur fugacity and temperature appear to be the main factors that controlled the PGE mineralogy during crystallization of the host chromitite in the upper mantle. If the activity of chalcogenides(such as S, and As) is low, PGE clusters will remain suspended in the silicate melt until they can coalesce to form alloys. Under appropriate conditions of ?S_2 and ?O_2, PGE alloys might react with the melt to form sulfides-sulfarsenides. Thus, we suggest that the Os, Ir and Ru metallic clusters and alloys in the Zedang chromitites crystallized first under high temperature and low ?S_2, followed by crystallization of sulphides of the laurite-erlichmanite, solid-solution series as the magma cooled and ?S_2 increased. The abundance of primary BMS in the chromitites suggests that ?S_2 reached relatively high values during the final stages of magnesiochromite crystallization. The diversity of the PGE minerals, in combination with differences in the petrological characteristics of the magnesiochromites, suggest different degrees of partial melting, perhaps at different depths in the mantle. The estimated parental magma composition suggests formation in a suprasubduction zone environment, perhaps in a forearc.  相似文献   

慢速扩张脊下的复杂熔- 岩相互作用：来自大西洋北纬14°97′区段洋中脊含铬铁矿纯橄岩的记录     

周翔  郑建平  熊庆  刘文龙  Henry J B Dick 《地质学报》2022,96(12):4242-4256

在大西洋洋中脊北纬14°97′附近贫岩浆型慢速扩张脊区段的洋底岩石调查中，拖网取样及洋底钻探均发现蛇纹石化地幔岩石中有脉状纯橄岩。纯橄岩中的铬铁矿粒度以毫米级为主，个别颗粒直径接近厘米级别，成分上显示中等程度的铬值与镁值(Cr#=52. 2~56. 1；Mg#=44. 6~51. 5)较高的TiO2含量(0. 60% ～0. 91%)。铬铁矿内部包裹体中大量出现韭闪石+金云母组合，并发现自形磷灰石包裹体。这些特征与“俯冲带型铬铁矿”的成分特征及矿物包裹体组合非常类似。本文的样品观察说明在洋中脊下方的熔体通道内，高度演化的熔体可以形成小体积的富水岩浆并参与铬铁矿的形成。拖网调查与钻探研究证实，研究区的纯橄岩、异剥橄榄岩、富橄榄石橄长岩、辉石岩、辉长岩及橄榄辉长岩等均以脉体形式产于难熔的大洋岩石圈橄榄岩质地幔中。这些脉状岩石共同记录了洋中脊玄武质熔体向上迁移过程中与围岩方辉橄榄岩间的熔- 岩反应，属于“交代橄榄岩”的范畴，揭示了慢速扩张洋脊之下熔体迁移诱发的复杂熔- 岩相互作用。  相似文献   

Chengdeite-A New Mineral of Ordered Natural Iron-iridium Alloy     

Yu Zuxiang Institute of Geology  Chinese Academy of Geological Sciences  Beijing 《《地质学报》英文版》1996,70(1):27-32

Chengdeite occurs in chromite orebodies in dunite as well as in placers in their neighbourhood. The mineral occurs as granular aggregates in association with inaglyite and in some cases occurs as graphic intergrowths with native iridium. It is opaque with a metallic lustre, colour steel-black, streak black,HM = 5.2, VHN50=452 kg/mm2, cleavage not observed, fracture not observed, strongly magnetic. Its reflection colour is bright white with a yellowish tint. It has no internal reflection, bireflectance or pleochrism, and shows isotropism.Thirteen chemical analyses were carried out by means of the electron microprobe. The mean percentages of the data obtained in the 13 analyses ares S 0.001, Fe 7.9, Ni 0.03, Co 0.03, Cu 0.83, As 0.02, Rh 0.19, Pd 0.00, Os 0.06, Ir 88.5, Ft 2.2 and Pb 0.00. The simplified formula is Ir3Fe, which requires Ir 91.17 and Fe 8.83, the total being 100.00 (% ).Five strongest lines of X-ray powder diffraction (hkl, d, I)are: 111, 2.18 (80);200, 1.89 (60); 220, 1.34 (70);311, 1.142  相似文献   

西藏普兰县姜叶马豆荚状铬铁矿地质特征及找矿前景   总被引：3，自引：0，他引：3  

雷义均  黄圭成  徐德明  李丽娟 《华南地质与矿产》2006,(3):55-60

姜叶马铬铁矿产于雅鲁藏布江超镁铁质岩带的西段拉昂错岩体之中,为富铬型豆荚状铬铁矿.本文主要讨论姜叶马豆荚状铬铁矿的地质特征及找矿前景.根据对拉昂错岩体岩相特征分析、姜叶马铬铁矿区已发现的豆荚状铬铁矿带和矿点的研究、以及与西藏罗布莎和东巧铬铁矿床的对比,总结了矿体分布和赋存规律,指出该地区具有形成大型豆荚状铬铁矿床的成矿地质条件,呈示出良好的找矿前景.  相似文献   

西藏铬铁矿接替资源航磁勘查及找矿方向探讨   总被引：1，自引：1，他引：1  

王德发刘英才  熊盛青薛典军范子梁  刘振军周坚鑫 《地质通报》2007,26(4):476-482

西藏是重要的铬铁矿产地,应用航磁圈定超基性岩,进行铬铁矿资源评价是国内外使用的常规方法,能快速缩小找矿靶区、取得事半功倍的效果。中国国土资源航空物探遥感中心于1969年在西藏中东部地区进行了1∶50万—1∶100万中等精度航磁概查,为早期铬铁矿勘查提供了间接信息;近年来又在中西部和一江两河(雅鲁藏布江、拉萨河和年楚河)及其北部地区进行了1∶100万—1∶20万高精度航磁调查。初步划分为5条强磁异常带和2个强磁异常群,为快速地发现超基性岩体、评价铬铁矿接替资源潜力提供了一批重要的间接找矿线索。  相似文献   

铬铁矿中的次近邻效应     

李哲  金明芝 《矿物学报》1990,10(2):186-191

本文使用穆斯堡尔效应对三个铬铁矿进行了研究,测量了铬铁矿L-1在150K和298K温度下的穆斯堡尔谱和铬铁矿L-2和L-3在298K温度下的谱。使用次近邻效应解释了铬铁矿中的多重Fe~(2+)双峰,并使用二项式分布计算了Cr~(3+)、Fe~(3+)和Al占据次近邻位置的几率。在穆斯堡尔面积和二项式分布计算的基础上做出了Fe~(2+)双峰的指派。铬铁矿L-1谱在150K下进一步分裂,表明用来解释铬铁矿谱的模型是正确的。  相似文献   

辽西豆荚状铬铁矿的发现及其意义   总被引：14，自引：0，他引：14  

李江海  牛向龙等 《岩石学报》2002,18(2):187-192,T001,T002

在辽西建平新太古代变质基底构造混杂带内首次识别出豆荚状铬铁矿。铬铁矿石显示特征的豆荚状构造、褶皱条带、透镜构造、豆状构造、拉长网孔构造等，它们可以与蛇绿岩内典型的豆荚状铬铁矿进行对比。依据同位素年龄制约，辽西豆英状铬铁矿形成于2．50Ga前后。结合该区已报道的新太古变基性火山岩具有大洋拉斑玄武岩成分特点、并广泛发育新太古代高压麻粒岩，可以认为辽西地区新太古代期间曾发生大规模的板块俯冲及碰撞作用过程。  相似文献