Geochemistry and zircon U-Pb chronology of quartz porphyry in Yuejinshan Fe-polymetallic deposit of Heilongjiang

Quartz porphyry in Yuejinshan Fe-polymetallic deposit is one of the rock masses, which formed the granite belt relating to the late Yanshanian skarn-type Fe-polymetallic deposits in the eastern Heilongjiang, and is also closely related to the metallogenic space of the Fe-polymetallic deposits. Quartz porphyry has the zircon U-Pb concordia age of 125.0±1.1 Ma, overall showing high Si(SiO_2=74.48%--75.00%), rich alkaline(Na_2O+K_2O=7.93%--8.17%, K_2O/Na_2O=1.39--1.46), and poor Mg(MgO=0.27%--0.31%), with the A/CNK value being 0.95--0.99, having the characteristics of obvious enrichment of LREE and medium Eu negative anomaly(0.69--0.74), indicating that the rock belongs to quasi-aluminous high potassium calc-alkaline series and has the same characteristics as those of the I-type granite. The rock is also characterized by the enrichment of LILE and active incompatible elements, and depletion of HFSE such as Nb, Ta, P and Ti, with the Mg~# value being 32--37, indicating that the rock originated from partial melting of crustal materials. It can be concluded from the above characteristics or data and from the distribution of contemporary magmatic rocks in the area, that quartz porphyry in Yuejinshan Fe-polymetallic deposit was formed in a tectonic background of the subduction of the paleo-Pacific plate in late Yanshanian.

Petrology and geochemistry of the Shilu Fe-polymetallic ore deposit in Hainan Province of South China: Implications for the origin of Neoproterozoic BIFs

The Shilu Fe-polymetallic ore deposit,a famous hematite-rich Fe-ore deposit,is situated at the western Hainan Province of south China.The deposit characterizes the upper Fe ores and the lower Co-Cu ores,which are mainly hosted within a low-grade to medium-grade,dominantly submarine metamorphosed siliciclastic and carbonate sedimentary succession of the Neoproterozoic Shilu Group.Three facies types of metamorphosed BIFs,i.e.the oxide facies,the silicate-oxide facies and the sulfide-carbonate facies BIFs,are identified within the sixth sequence of the Shilu Group.The oxide facies BIF(i.e.the Fe-rich itabirites or ores)consists of alternating hematite-rich microbands with quartz-rich microbands;the silicate-oxide facies BIF(i.e.the Fe-poor itabirites or ores)comprises alternating millimeter-to a few tens meter-scale,magnetite-hematite-rich bands with calcsilicate-rich(garnet+actinolite+diopside+epidote+quartz)meso-to microbands;and the sulfide-carbonate facies BIF(i.e.the Co-Cu ores)contains alternating macro-to mesobands of Co-bearing pyrite and pyrrhotite,and chalcopyrite with mesobands of dolomite+calcite+diopside+quartz and/or chlorite+sericite+quartz.The blastooolitic,blastopelletoid blastocolloidal and blastopsammitic textures,and blasobedding structures which most likely represent primary sedimentation are often observed in these BIF facies.The interbedded host rocks with the BIFs mainly are the pyroxene-amphibole rocks and the banded or impure dolostones,and also contain banded or laminated structures,and lepido-gra-noblastic,nematoblastic and/or blastoclastic textures.Compositionally,the main host rocks,the pyroxene-amphibole rocks contain basic-intermediate SiO_2(~54.00 wt.%),CaO(~14.19 wt.%),MgO(~9.68 wt.%)and Al_2O_3(~8.49 wt.%)with a positive correlation between Al_2O_3 and TiO_2.The UCC-like Zr and Hf abundances,high Ba content andεNd(t)value(^-5.99)as well as the ratios of La/YbPAAS(0.17~1.00),δEuPAAS(0.88~1.12)andδCePAAS(0.93~1.13)commonly reveal that the protoliths to this type rocks are hydrogenic with a large contribution of terrigenous sediments and minor hydrothermal input.The high CaO+MgO+LOI contents and the extremely low trace element and REEconcentrations as well as the ratios of Y/Ho(44~45),δEuPAAS(1.13~1.57)andδCePAAS(0.69~0.98)reflect a marine origin with minor terrigenous materials for the banded or impure dolostones.Moreover,this type rocks also account for a negativeεNd(t)value(^-7.49).The oxide facies BIF is dominated by Fe_2O_3+FeO(~75.59wt.%)and SiO_2(~20.47 wt.%)with aεNd(t)value of^-6.10.The variable contents in Al_2O_3,TiO 2,K2O,Na2O,Zr,Hf and∑REE,and variable ratios of Y/Ho(24~39)andδEuPAAS(0.86~11.07)suggest the precursor sediments to this facies BIF are admixtures of sea-floor hydrothermal fluids and seawaters with minor involvement of detrital components.Compared to the oxide facies BIF,the silicate-oxide facies BIF is lower in Fe_2O_3+Fe O(~39.81wt.%)and Ba but higher in SiO_2(~42.54 wt.%),Al2O3(~3.60 wt.%),TiO_2(~0.19 wt.%),MgO(~1.12 wt.%),CaO(~9.06 wt.%),K_2O(~0.98 wt.%),Mn and Zr.The ratios of Y/Ho(25~34),La/YbPAAS(0.14-0.74)andδEuPAAS(0.91~1.12)most likely are linked to higher degree of detrital contamintants.While the sulfide-caronate facies BIF is main but variable in Fe_2O_3+Fe O(15.79~57.91 wt.%),SiO 2(0.54~61.52 wt.%),MgO(0.12~16.09wt.%),CaO(0.17~23.41 wt.%)and LOI(8.28-30.06 wt.%).The generally low contents in trace elements(including REE)except for an obvious enrichment in Pb,and the positive Ce anomalies(δCePAAS=1.04~1.95)and negative Pr anomalies(δPrPAAS=0.67~0.93),as well as the variable ratios ofδEuPAAS(0.72~1.71),La/YbPAAS(0.26~1.60)and Y/Ho(26~57)suggest that the precursors to the sulfide-carbonate facies BIF mainly are metalliferious sediments from deep-marine hydrotheral source with minor detrital components.The T2DM ages(ca.2.0 Ga)imply that the Shilu BIFs and interbedded host rocks contain a component with Paleoproterozoic crustal residence age due to a significant crustal accretion event at ca.2.0 Ga in Hainan Island.In connection with the petrographical and mineralogical relationship,we conclude that the precursor precipitates to the Shilu BIFs are variable degree of admixtures of the Fe-Co-Cu-(Si)-rich hydrothermal fluids and detrital components from seawater and fresh water carring continental landmass;whereas the protolith to the main interbedded host rocks,i.e.the pyroxene-amphibole rocks,most likely was terrigenous,fine-grained clastic-sediments but with significant input of hydrothermal fluids in a seawater environment.As a result,a continent marginal marine basin is proposed for deposition of the Shilu BIFs and interbedded host rocks.Sea-level fluctuations caused by marine transgression–regressions possibly contributed to changes in the composition and varied input of the terrigenous sediments.

完达山地块跃进山矽卡岩型铜金矿区酸性侵入岩锆石U-Pb年龄、地球化学特征及成因

跃进山小型矽卡岩型铜金矿床位于完达山地体西南部,矿体主要赋存于矽卡岩、花岗斑岩及其构造裂隙中,呈扁豆状或脉状。本文对矿区花岗闪长岩和花岗斑岩进行锆石U-Pb年代学和岩石地球化学研究,以了解矿床形成时代、成岩(矿)构造背景及矿床成因。测年结果表明,花岗斑岩和花岗闪长岩成岩年龄分别为(115.8±1.0)Ma和(126.9±1.7)Ma,铜金矿化时代与花岗斑岩成岩时代基本一致,为早白垩世晚期。岩石地球化学研究表明,花岗闪长岩属过铝质钙碱性系列岩石,稀土配分模式图为轻稀土富集,重稀土亏损,具较强的铕负异常,无铈异常,岩浆主要来源于壳源物质;花岗斑岩属过铝质钙碱性系列岩石,轻稀土富集,重稀土亏损,具弱铕负异常,无铈异常,相对富集大离子亲石元素(Rb、Ba、K、Sr)和不相容元素(U、Th),亏损高场强元素(Ta、Nb、P、Ti)和HREE,岩浆来源于壳幔物质混合源区,形成于碰撞后构造环境,成岩成矿作用与太平洋板块强烈俯冲作用后的伸展体制密切相关。

黑龙江省跃进山铜金矿床花岗斑岩锆石U-Pb定年及地质意义

跃进山铜金矿床是完达山活动带的典型矿床,位于密山—敦化深断裂北侧。本文对含矿花岗斑岩开展了锆石LA-ICP-MS U-Pb测年、主量和微量元素的研究,厘定岩体的形成时代,探讨了成矿构造背景。结果表明与成矿密切相关的花岗斑岩的年龄为(109.17±0.91)Ma。它们为过铝质钙碱性系列岩石,富集Rb、Ba、La、Nd、Hf等元素,亏损Nb、Sr、P、Ti等元素,具俯冲带岩浆岩的基本特征,这些暗示它们形成于岛弧或活动大陆边缘环境。结合岩体的地球化学特征和完达山成矿带的构造岩浆演化,认为该矿床形成于岛弧构造背景,其形成与中生代太平洋的俯冲及早白垩世晚期东亚东部岩浆活动陆缘迁移、构造单元转化有关。

黑龙江跃进山矽卡岩型铜金矿床花岗闪长岩的年代学和地球化学特征

对跃进山铜金矿床与矽卡岩型矿化有关的花岗闪长岩开展了LA-ICP-MS锆石U-Pb定年、锆石Lu-Hf同位素及岩石地球化学研究。结果表明,花岗闪长岩中26个锆石测点的^(206)Pb/^(238)U加权平均年龄为(118.96±0.77) Ma (MSWD=0.29);岩体中锆石的ε_(Hf)(t)值均为正值(+1.4~+3.2),且具有较年轻的Hf二阶段模式年龄(t_(DM2)=1.09~0.98 Ga);花岗闪长岩表现为富Al、高K和Na以及低Ti、P、Ca的钙碱性I型花岗岩地球化学特征,显示出轻稀土富集、重稀土元素亏损的稀土元素组成特征;样品锆石的ε_(Hf)(t)的值为偏低的正值,表明岩浆物质来源应为壳幔混源。结合岩石地球化学投图以及区域构造背景演化认为,花岗闪长岩和花岗斑岩均属于后碰撞-火山弧花岗岩,研究区的成矿成岩作用与太平洋板块强烈俯冲背景下的下岩石圈地幔拆沉有直接关系。

综合物探方法在青海省跃进山铁矿勘查中的应用

以跃进山铁矿为研究对象,利用地面高精度磁测和可控源音频大地电磁法两种方法的联合勘查,达到了最终的勘查目的。本区的地质、物探实际勘查工作表明,针对地形困难和地质特殊的测区,选择适合指导本区地质找矿的物探工作方法至关重要,它直接影响到最终的勘查效果。实践证明,在本区综合运用地面高精度磁测和可控源音频大地电磁测深取得了良好的地质找矿效果。通过深入研究综合物探异常,结合研究区地质特征对矿床的找矿前景做出了综合评价,建立了矿区的地质—地球物理找矿模型,可为成因类型相似或相同地区找矿提供借鉴意义。