华北克拉通小秦岭地区元古宙正长岩LA-ICP-MS锆石U-Pb年龄及其地质意义

小秦岭地区是华北克拉通中央带南部一个重要组成部分。关于其地壳组成、变质作用,尤其是岩浆作用年龄的研究,对确认小秦岭地区在1.85～1.70 Ga期间大地构造是非常重要的。报道了小秦岭地区北部古元古代正长岩LA-ICP-MS锆石 U-Pb平均年龄为（1 831.0±6.8）Ma(95%可信度,MSWD=0.37);结合年龄数据和地质证据,认为小秦岭地区（1 831.0±6.8）Ma正长岩形成于华北克拉通南缘地壳减薄作用环境之中,可能也是大火成岩省的一个组成部分,并探讨了华北克拉通在1.90～1.85 Ga和1.85～1.70 Ga 期间的演化历史。     

New paleomagnetic data on the Anabar Uplift and the Uchur-Maya region and their implications for the paleogeography and geological correlation of the Riphean of the Siberian Platform

The results of paleomagnetic studies of the reference sections of the Riphean and Late Proterozoic intrusive bodies of two remote areas of the Siberian Platform are presented. Within the limits of the Uchur-Maya region the sedimentary rocks of the Gonam, Omakhta, Ennin and Konder formations were studied; and the Riphean sedimentary rocks of the Burdur and Kotuykan formations on the northern and western slopes of the Anabar Uplift and, also, the Late Proterozoic intrusive complexes, located in the basins of the Fomich, Magan, Dzhogdzho and Kotuykan Rivers were studied. The paleomagnetic poles obtained in the course of this work and the present-day geochronological data give grounds to assume that: (1) the accumulation of the Riphean of the Anabar Uplift occurred after the formation of the Uchurskaya series of the Uchur-Maya region and was completed in approximately 1.5 Ga; (2) the Konder layers, compared according to the correlation pattern accepted at the present time [Semikhatov and Serebryakov, 1983] with the bottoms of the Totta formation, can be related to the appreciably more ancient stratigraphic level; (3) the intrusion of the studied intrusive bodies of the northern and western slopes of the Anabar Uplift occurred nonsimultaneously, although within close time intervals of approximately 1.5 Ga. The estimates of the kinematic parameters of the drift of the Siberian Platform within an interval of 1.7–1.0 Ga is carried out.     

澳大利亚兰杰一号铀矿之生命周期：地质、资源、生产与修复

兰杰一号铀矿及其所属的鳄鱼河铀矿田产于北澳太古宙克拉通内古元古代裂谷背景下发展起来的松溪造山带,矿体产于新太古代—古元古代结晶-变质基底/晚古元古代—中元古代康博尔吉红层建造不整合界面之下,铀矿化分3个时代,U_1为1720～1680Ma,U_2为1420～1040Ma,U_3为474±6Ma,U1是主矿化时代。该矿床于1969年后期通过航空放射性测量被发现,1970’s经勘探圈定了No.1和No.3两个铀矿体,总计资源储量124681t@0.23%U_3O_8。1980年10月正式露采,至2018年12月,总计生产了128739t U_3O_8。1985财年开始,ERA(澳大利亚能源资源有限责任公司)向世界核能市场共计销售了产于兰杰铀矿的119882t U_3O_8。2009年,发现了No.3深部矿,探明资源储量为43857t@0.22%U_3O_8,这部分资源将以地下开采方式利用。预计到2026年,采区地貌景观和生态环境将得到恢复。进一步讨论了澳北元古宙不整合面型铀矿找矿的方向,持续稳定的铀矿开采与生产的意义,以及投资澳大利亚铀矿业需要注意的政治与法律问题。这些内容可以为国内矿业企业及地勘单位合理部署澳洲铀矿勘查与开发提供参考。     

元古代蛇绿岩及铬铁矿

本文总结了国外典型元古代蛇绿岩的岩石组合、野外产状、地球化学资料以及成矿特征,并与显生宙蛇绿岩进行了对比,继而探讨元古代板块构造演化和铬铁矿成因。资料表明,早元古代和中-新元古代均有蛇绿岩的存在,但前者较少,仅见于Canadian地盾的Cape Smith Belt中的Prutuniq蛇绿岩(2. 05～2. 0Ga)和芬兰Fennoscandian地盾的Outokumpu和Jormua蛇绿岩(时代为1. 97～1. 96Ga),而中-新元古代的蛇绿岩则见于世界许多地区,如埃及东部沙漠区(～750Ma)和非洲东北部地区(ca.900～800Ma)等。与显生宙蛇绿岩相比,这些老蛇绿岩具如下特征:(1)它们均为被肢解的蛇绿岩,大多与"弧火山岩"和(或)混杂岩伴生,经历不同程度的变形和变质(具绿片岩相-角闪岩相组合);(2)岩石组合大多较齐全,壳层组合发育,以镁铁-超镁铁岩(堆晶岩)、辉长岩、镁铁质席状岩床(墙)杂岩、火山岩为代表;层状镁铁-超镁铁岩的韵律层以及矿物的隐晶变化等均提示了岩浆多期次活动及开放岩浆房的特征;(3)元古代蛇绿岩中既有高铝型铬铁矿,也有高铬型铬铁矿,且主要寄主于纯橄岩(或蛇纹岩)中;高铝型和高铬型直接受控于熔体的熔融程度及含水流体的参与,反映了铬铁矿形成于俯冲带演化的不同阶段;铬铁矿规模均较小,且均以低TiO 2为特征,均为岩浆分异作用的产物,明显区别于显生宙熔融残余成因的豆荚状铬铁矿;(4)元古代蛇绿岩常伴有硫化物Cu-Co-Zn-Au矿,且铬铁矿含Zn较高(Zn=0. 11%～0. 18%)(如芬兰Outokumpu蛇绿岩);橄榄岩及铬铁矿中常含较高的MnO (高达1. 79%,如埃及东部的Wizer蛇绿岩);(5)元古代蛇绿岩具多种成因:主要为俯冲带成因(如埃及蛇绿岩、北东非蛇绿岩、芬兰Outokumpu蛇绿岩),少量为洋中脊成因(加拿大Purtuniq蛇绿岩)及裂谷成因(芬兰Jormua蛇绿岩)等。     

Calcite twinning strain variations across the Proterozoic Grenville orogen and Keweenaw-Kapuskasing inverted foreland,USA and Canada

We report the calcite twinning strain results of a traverse across the Grenville orogen from Parry Sound, Ontario (NW) to Ft. Ann, New York (SE), including the younger, adjacent Ordovician Taconic allochthon. Fifty four carbonates (marbles, calcite veins, Ordovician limestone) were collected resulting in 68 strain analyses on mechanically twinned calcite (n = 2337 grains) across the Central Gneiss Belt (CGB; 3 samples), the Central Metasedimentary Belt (CMB; 27 samples), the Central Granulite Terrane (CGT; Adirondack's; 13 samples) and the Ottawan Orogenic Lid (OOL; 11 samples). Twinning strains in the greenschist-grade OOL marbles preserve N–S shortening and U-Pb titanite ages (～1150 Ma; n = 4) document these marbles formed during the Shawinigan (1190–1140 Ma) part of the Grenville orogen. From northwest to southeast, the Ottawan (1095–1020 Ma) twinning strain is dominantly a layer-parallel shortening fabric oriented N–S (Parry Sound), then becomes parallel to the Grenville thrust direction (NW–SE) across the CMB to the Adirondack Highlands where the sub-horizontal shortening strain becomes margin-parallel (SW–NE). Within the regional sample suite there are two areas studied in detail, the Bancroft shear zone (n = 11) and a roadcut on the southeast side of the Adirondack Mountains (Ft. Ann, NY; n = 8). Marbles from the Bancroft shear zone contain calcite grains with 2 sets of twin lamellae (e₁ and e₂). The better-developed e₁ sets (n = 406) record a horizontal fabric oriented NW–SE whereas the younger e₂ lamellae (n = 146) preserve a margin-parallel (SW–NE) horizontal fabric. Both the e₁ and e₂ strains record an overprint vertical shortening strain (NEV), perhaps related to extensional orogenic collapse. We also report an Ottawan orogen-aged granoblastic mylonite (1093 Ma, U-Pb zircon; 1102 Ma Ar-Ar biotite) in the Keweenaw thrust hanging wall 500 km inboard of the Grenville front and interpret the relations of Grenville-Keweenaw far-field dynamics.     

江西弋阳铁砂街中元古代海底火山喷流成矿作用

江西弋阳铁砂街铜矿产于中元古代晚期海相火山岩中,矿床在大地构造环境、含矿地层建造、矿体形态、喷流岩组合、喷流岩主量－微量－稀土元素地球化学、同位素地球化学方面都具有海底火山喷流沉积的典型特征,是扬子板块、华夏板块边缘中元古代裂谷海底火山喷流沉积作用的产物。     

The Origin of the Proterozoic Bidjovagge Gold-Copper Deposit, Finnmark, Northern Norway, as Deduced from Rare Earth Element and Nd Isotopic Evidences on Calcites

Abstract: The Bidjovagge gold-copper deposit, northern Norway occurs in the lower Proterozoic Kautokeino greenstone belt, and consists of ten ore bodies in albite felsite, graphite schist and meta-diabase sills, along with a series of syenodiorite dykes. Calcite is one of the most important gangue minerals occurring within the ore veins. The early primary calcite samples from A, C and D ore bodies (copper–rich) show almost flat chondrite-normalised REE curves, and slightly positive Eu anomalies. A Sm-Nd isotope age of 1858 ± 72 Ma (2ρ) has been given based on fifteen primary calcite samples. The Sm-Nd age of calcite is in well agreement with previously published U-Pb davidite age of 1885 ±18 Ma (2ρ) and Sm-Nd davidite age of 1886 ± 88 Ma (2ρ). All these isotopic age data indicate that the gold-copper mineralisation may occur during or slightly after the peak of the Svecokarelian orogeny. Two late primary calcite samples from C and D ore bodies have flat chondrite-normalised LREE curves, positive HREE curves, and negative Eu anomalies. In contrast, most of the early primary calcite samples from B ore body (gold–rich) show an overall negative chondrite-normalised REE slope and negative Eu anomalies. Sm-Nd data on seven primary calcite samples from the B ore body are relatively scattered, and gave an isochrone age of 1809 ± 150 Ma (2ρ), identical to the age of the calcite samples from A, C and D ore bodies. Two late primary calcite samples from the B ore body have almost flat chondrite-normalised REE slope and negative Eu anomalies. REE patterns and eNd (T) values of calcites suggest that the ore fluids for the calcites from the A, C and D ore bodies derived their metals from mafic igneous rocks (diabase sills). For the secondary calcites from the C ore body, their relative high initial Nd (T) values at 1858 Ma imply that much more radiogenic Nd-component were incorporated during calcite crystallisation when another ore fluid emplaced. Combined Nd isotope data and REE geochemical features suggest that the isotopically more evolved source such as albite felsite and syn-genetic high level syenodiorite dykes were probably metal source for these calcites in the B ore body. Three samples of secondary calcite from the B ore body, which obviously deviated from 1809 Ma isochron are easily explained as products of post-ore hydrothermal events.     

辽宁宽甸刘家堡子超单元岩浆演化

刘家堡子超单元同位素锆石Ｕ－ Ｐｂ 一致线年龄值为２ ０４６．４８±７ ．０１Ｍａ,侵位时代为古元古代。按照侵入岩岩石谱系单位的划分原则,由早至晚划分为红旗村单元石英闪长岩、头道阳岔单元花岗闪长岩及阳隈子单元二长花岗岩,归并为刘家堡子超单元。成因类型为Ⅰ型花岗岩类,成岩物质来源于下地壳,岩浆演化由中性至酸性,演化明显,构成了完整的演化序列。     

内蒙古狼山造山带构造演化与成矿响应

狼山造山带位于华北地台北缘西段,它经历了新太古代和古元古代结晶基底形成与变形、中元古代被动陆缘裂陷槽裂解→沉积→闭合、新元古代晚期开始的活动陆缘、海西期→中生代以来的挤压造山并伴有大量中酸性岩浆侵入的漫长构造演化与发展过程。该造山带有丰富的锌、铅、铜、铁、金等矿产资源,矿床(化)类型、矿床规模与时空分布规律都与其成矿地质背景、构造演化有密切的耦合关系,在不同构造演化阶段有不同的矿床形成:在新太古代主要形成了海底火山环境热水沉积条带状铁矿、在中元古代主要形成了与被动陆缘裂解过程相关的海底啧流.沉积铅锌铜铁硫化物矿床、而在海西期—中生代以来挤压造山过程中的岩浆热液活动,既形成了中小型的斑岩型铜金矿床、又对中元古代等先成的喷流-沉积矿床产生了明显的改造和叠加成矿作用。东升庙、炭窑口和霍各乞矿床的部分铜矿是造山过程中叠加成矿的结果。     

Carbonatitic Volcanic Genesis of Hetaoqing Fe-Cu Deposit in Central Yunnan, China

Abstract. The Kunyang rift on western margin of Yangtze Platform is a continental rift, and also a rare Precambrian Fe-Cu mineralization zone in China. The Wuding-Lufeng mineralization area in the middle section of the rift is an important part of the zone, and an elliptic-shaped volcanic collapsed basin, controlled by a ring fracture system with carbonatitic volcanic rocks mainly occurring along the northwestern edge of the basin. The Hetaoqing Fe-Cu ore deposit at the western side of the basin is hosted in carbonatitic volcanic rocks and pyroclastic sedimentary rocks. The original ore bodies occur as layers, bands and lenses conformable to the host carbonatitic rocks. The ores usually appear as massive, impregnated and granular in carbonatitic rocks, and as brecciform and sandy in pyroclastic sedimentary rocks. Ore-forming minerals are magnetite, hematite, chalcopy-rite, bornite, pyrite, carrollite, molybdenite, cobaltite and skinnerite, and secondary minerals limonite, chalcocite, azurite, malachite and tenorite. Gangue minerals are calcite, dolomite, ankerite, common hornblende, arfvedsonite, augite, aegirine-augite, albite, phlogopite, biotite, chlorite and apatite. Evidences of mineral chemistry, trace elements and isotopic ratios of ores, as well as geological features, suggest that the original ores are igneous in origin. Chemical features of magnetites in the deposit belong to carbonatite type, and are similar to those from the Bayan Obo carbonatites. The ores are rich in iron, titanium, rare earth elements, niobium, tantalum, gold, silver, phosphor and sulfur. These features indicate that the Fe-Cu deposit associated with volcanic activity in the Wuding-Lufeng basin is alkali-carbonatite volcanic type.