Ag-rich Tetrahedrite in the El Zancudo Deposit,Colombia: Occurrence,Chemical Compositions and Genetic Temperatures

Chemical compositions of tetrahedrite—Ag-rich tetrahedrite—freibergite solid solutions (Ag-rich tetrahedrite_ss) and homogenization temperatures of fluid inclusions in quartz and carbonates of seventeen samples from nine veins in the El Zancudo deposit, Antioquia, Colombia, were investigated to reveal the origin of silver in Ag-rich tetrahedrite_ss, to derive their crystallization temperatures and to examine the relationship between chemical compositions of Ag-rich tetrahedrite_ss and their crystallization temperatures. The ores consist of arsenopyrite, pyrite, sphalerite, Ag-rich tetrahedrite_ss, galena, boulangerite, andorite, owyheeite, diaphorite, jamesonite, miargyrite, bournonite, chalcopyrite, and electrum. Ag-rich tetrahedrite_ss forms about 10 volume % of the total ores and is one of the most common and widely distributed sulfosalts in this deposit. Ag-rich tetrahedrite_ss is rich in Ag (1.13 to 31.02 wt%) and Sb (22.93 to 29.82 wt%), and poor in As (0.06 to 2.43 wt%), consistent with the reported incompatibilities of Ag and As in Ag-rich tetrahedrite_ss. The Zn/(Zn + Fe)-, Ag/(Ag + Cu)- and Sb/(Sb + As + Bi)-atomic ratios exhibit some variations among the veins. Ag-rich tetrahedrite_ss with higher Ag/(Ag + Cu) ratios coexist with diaphorite, whereas those with lower ratios are not associated with this sulfosalt. Ag-rich tetrahedrite_ss in the assemblages of Ag-rich tetrahedrite_ss+ sphalerite and of Ag-rich tetrahedrite_ss+ bournonite + galena shows no Zn ↔ Fe and Cu ↔ Ag variations between core and rim, respectively, negating the possibility of solid state reaction during cooling. Ag-rich tetrahedrite_ss is thus regarded as primary phase. Homogenization temperatures of primary fluid inclusions in quartz and carbonates co-existing with Ag-rich tetrahedrite_ss define the mineralization temperatures of 134 to 263°C. Independent crystallization temperatures of Ag-rich tetrahedrite estimated based on Zn/(Zn + Fe) and Ag/(Ag + Cu) ratios of the Ag-rich tetrahedrite_ss associated with silver minerals such as miargyrite, andorite and diaphorite using Sack's thermochemical database lie in a range between 170 and ∼250°C. Both results are thus in good agreement.     

Mineral and geochemical compositions,regularities of distribution,and specific formation of ore mineralization of the Rogovik gold-silver deposit (northeastern Russia)

New data on the mineral composition and the first data on the geochemical composition of ores of the Rogovik gold-silver deposit (Omsukchan ore district, northeastern Russia) have been obtained. Study of the regularities of the spatial distribution of ore mineralization shows that the deposit ores formed in two stages. Epithermal Au-Ag ores of typical poor mineral and elemental compositions were generated at the early volcanic stage. The major minerals are low-fineness native gold, electrum, acanthite, silver sulfosalts, kustelite, and pyrite. The typomorphic elemental composition of ores is as follows: Au, Ag, Sb, As, Se, and Hg. The content of S is low, mostly < 1%. Silver ores of more complex mineral and elemental compositions were produced under the impact of granitoid intrusion at the late volcanoplutonic stage. The major minerals are high-Hg kustelite and native silver, silver sulfosalts and selenides, fahlore, pyrite, chalcopyrite, galena, and sphalerite. The typomorphic elemental composition of ores is as follows: Ag, As, Sb, Se, Hg, Pb, Zn, Cu, and B. The content of S is much higher than 1%. The ores also have elevated contents of Mo, Ge, F, and LREE (La, Ce, and Nd). At the volcanoplutonic stage, polychronous Au-Ag ores formed at the sites of the coexistence of silver and epithermal gold-silver mineralization. Their specific feature is a multicomponent composition and a strong variability in chemical composition (both qualitative and quantitative). Along with the above minerals, the ores contain high-Hg gold, hessite, argyrodite, canfieldite, orthite, fluorapatite, and arsenopyrite. At the sites with strongly rejuvenated rocks, the ores are strongly enriched in Au, Ag, Hg, Cu, Pb, Zn, Ge, Se, La, Ce, Nd, S, and F and also contain Te and Bi. The hypothesis is put forward that the late silver ores belong to the Ag-complex-metal association widespread in the Omsukchan ore district. A close relationship between the ores of different types and their zonal spatial distribution have been established. In the central part of the Rogovik deposit, epithermal Au-Ag ores are widespread in the upper horizons, Ag ores are localized in the middle horizons, and rejuvenated polyassociation Au-Ag ores occur at the sites (mostly deep-seated) with ore-bearing structures of different ages.     

河南洛宁沙沟Ag-Pb-Zn矿床银的赋存状态及成矿机理

位于河南洛宁境内的沙沟热液脉型Ag-Pb-Zn矿床是熊耳山地区近年来新发现的大型矿床.野外观察和矿相学研究表明成矿过程包含4个阶段, 分别为石英-菱铁矿阶段(Ⅰ)、石英-闪锌矿阶段(Ⅱ)、石英-银矿物-方铅矿阶段(Ⅲ)和石英-碳酸盐阶段(Ⅳ), 其中Ⅱ、Ⅲ阶段为主成矿阶段.扫描电子显微镜-能谱分析(SEM-EDS)和电子显微探针微区成分分析(EMP)结果显示, 沙沟矿床中的银以不可见银和可见银两种形式存在, 但以可见银为主.不可见银主要以次显微包体(< 1 μm)的形式被包裹在黄铜矿和闪锌矿等硫化物中, 而可见银通常以各种银的独立矿物形式交代方铅矿和黄铜矿等硫化物或充填在硫化物和石英的显微裂隙内.结合本文研究和前人对沙沟矿床流体包裹体的研究认为, 银和铅、锌等金属离子在成矿早期高温阶段以氯络合物的形式搬运, 随着成矿热液温度和氧逸度的降低以及pH值的升高, 氯络合物因稳定性降低而解体, 硫氢络合物成为银、铅、锌的主要迁移形式.随着成矿热液温度的继续降低, 铅、锌等金属硫氢络合物开始分解, 方铅矿、黄铜矿和闪锌矿等硫化物得以沉淀, 此时部分银以显微和次显微包体银的形式被包裹于这些硫化物中.铅锌硫化物的大量沉淀引起成矿热液组成和性质的显著变化, 最终导致银从硫氢络合物中彻底解体, 并与Cu+、Sb3+等离子结合形成大量独立银矿物(如含银黝铜矿、硫锑铜银矿和辉铜银矿等), 而溶液中过饱和的银则以自然银的形式沉淀.      

湘西沃溪钨锑金矿床超纯自然金

湘西沃溪钨锑金矿床产有自然界中十分罕见的超纯自然金。超纯自然金的Au含量在99 %以上 ,Fisher成色接近1000。自然金中含有Ag、Pb、Zn、Cu、As、Sb、Hg、Bi等显微化学组分。与一般自然金相比 ,超纯自然金的Ag 含量显著偏低 ,而Pb、Zn、As、Sb、Hg、Bi等显微化学组分含量趋于偏高 ,且较稳定。理论分析表明 ,超纯自然金的形成与强氧化性的酸性成矿流体有关。流体中金、银主要以MeCl2-(Me=Au或Ag)的络合物形式迁移。推断矿床成矿可能与区域中酸性岩浆活动有成因联系。     

个旧锡矿区方铅矿的某些成因矿物学特征及其找矿意义

个旧方铅矿颜色深,光泽暗者含银高,银以类质同象赋存者反射率高,硬度与晶胞参数呈正相关。方铅矿主元素含量及Pb/S比值反映矿区低铅亏硫的成矿环境。锡含量及红外光谱谱线可作为深部锡矿床的判别标志。方铅矿中银以独立矿物的形式赋存或(Bi/Ag)<0.001％的矿床,银可具工业价值。晶胞参数随成矿温度的降低而增大。稳定同位素表明成矿物质多源。     

大兴安岭中段铜多金属矿床矿物微量元素研究

对大兴安岭中段铜多金属矿床硫化物矿同量元素研究表明,虽然该区矿床类型不同,但闪锌矿种属一致,多为铁闪锌矿和含铁闪锌矿,而方铅矿中Ｓｂ,Ｂｉ,Ａｇ含量却明显不同;黄铜矿中的Ｃｏ,Ｎｉ含量明显大于黄铁矿中的Ｃｏ,Ｎｉ含量;各类型矿床中方铅矿,闪锌矿,黄铜矿,黄铁矿等硫化物中Ａｇ普遍有较高的含量,反映了大兴安岭中段银处于高异常区,银,金,镉,铟往往具有综合利用价值。     

攀西裂谷带铅-锌矿床中方铅矿的一些成因特征

本文主要从方铅矿中微量元素的含量和晶体化学的一些特征来讨论攀西裂谷带铅锌矿床的成因。方铅矿中具有成因指示意义的元素是Bi和Sb,研究表明,在方铅矿中Bi/Sb>1000时,其成因为中—高温热液类型,在Bi/Sb<1时为低温型或层控式。因此可根据该比值来确定矿床成因类型及成矿温度。Bi和Sb在方铅矿中替代Pb时,方铅矿晶格有缺位,这一晶体化学特征可解释在方铅矿中Ag与Bi、Sb含量间不一定呈正相关。     

Silver-Bearing and Associated Minerals in El Zancudo Deposit, Antioquia, Colombia

The occurrence and the chemical compositions of ore minerals (especially the silver‐bearing minerals) and fluid inclusions of the El Zancudo mine in Colombia were investigated in order to analyze the genetic processes of the ore minerals and to examine the genesis of the deposit. The El Zancudo mine is a silver–gold deposit located in the western flank of the Central Cordillera in Antioquia Department. It consists mainly of banded ore veins hosted in greenschist and lesser disseminated ore in porphyritic rocks. The ore deposit is associated with extensive hydrothermally altered zones. The ores from the banded veins contain sphalerite, pyrite, arsenopyrite, galena, Ag‐bearing sulfosalts, Pb‐Sb sulfosalts, and minor chalcopyrite, electrum, and native silver. Electrum is included within sphalerite, pyrite, and arsenopyrite, and is also partially surrounded by pyrite, arsenopyrite, sphalerite, and tetrahedrite. Native silver is present in minor amounts as small grains in contact with Ag‐rich sulfosalts. Silver‐bearing sulfosalts are argentian tetrahedrite–freibergite solid solution, andorite, miargyrite, diaphorite, and owyheeite. Pb‐Sb sulfosalts are bournonite, jamesonite, and boulangerite. Two main crystallization stages are recognized, based on textural relations and mineral assemblages. The first‐stage assemblage includes sphalerite, pyrite, arsenopyrite, galena and electrum. The second stage is divided into two sub‐stages. The first sub‐stage commenced with the deposition and growth of sphalerite, pyrite, and arsenopyrite. These minerals are characterized by compositional growth banding, and seem to have crystallized continuously until the end of the second sub‐stage. Tetrahedrite, Pb‐Cu sulfosalts, Ag‐Sb sulfosalt, and Pb‐Ag‐Sb sulfosalts crystallized from the final part of the first sub‐stage and during the whole second sub‐stage. However, one Pb‐Ag‐Sb sulfosalt, diaphorite, was formed by a retrograde reaction between galena and miargyrite. The minimum and maximum genetic temperatures estimated from the FeS content of sphalerite coexisting with pyrite and the silver content of electrum are 300°C and 420°C, respectively. These estimated genetic temperatures are similar to, but slightly higher than the homogenization temperatures (235–350°C) of primary fluid inclusions in quartz. The presence of muscovite in the altered host rocks and gangue suggest that the pH of the hydrothermal solutions was close to neutral. Most of the sulfosalts in this deposit have previously been attributed as the products of epithermal mineralization. However, El Zancudo can be classified as a xenothermal deposit, in view of the low pressure and high temperature genetic conditions identified in the present study, based on the mineralogy of sulfosalts and the homogenization temperatures of the fluid inclusions.     

Study on the Cu–As–Sb–Ag–Bi–Pb–Te Sulfosalt Minerals from the Hydrothermal System of Southwestern Hokkaido,Japan

Shin‐Otoyo, Suttsu, Teine, Date, Chitose, and Koryu are sites rich in precious and base metal Miocene–Pleistocene epithermal deposits, and located in southwestern Hokkaido, Japan. The deposits are predominantly hosted by the Green Tuff Formation of Middle Miocene age. Ore petrographic study of these deposits shows the occurrence of variable quantities of Cu–As–Sb–Ag–Bi–Pb–Te sulfosalt minerals. Determination of mineralogical and chemical compositions of the sulfosalt minerals was undertaken to elucidate the time and spatial changes of the sulfide‐sulfosalt minerals. Various types of sulfosalt minerals identified from gold–silver and base metal quartz–sulfide veins represented some sulfosalt mineralization phases, such as the Cu–Fe–Sn–S phase of mawsonite and stannite; Cu–(As,Sb)–S phase of tetrahedrite–tennantite and luzonite–famatinite series minerals; (Cu,Ag)–Bi–Pb–S phase of emplectite, pavonite, friedrichite, aikinite, and lillianite–gustavite series minerals; (Ag,Cu)–(As,Sb)–S phase of proustite–pyrargyrite and pearceite–polybasite series minerals; and Bi–Te–S phase of tetradymite and kawazulite minerals. There are some trends in the paragenetic sequence of sulfosalt mineralization in southwestern Hokkaido (in complete or partial) as follows: sulfide → Cu–Fe–Sn–S → (Cu,Ag)–Bi–Pb–S → (Bi–Te–S) → Cu–(As,Sb)–S → ([Ag,Cu]–[As,Sb]–S). The formation of sulfosalt minerals is characterized by the introduction of some elements such as Sn, Bi, and Te at an earlier stage and an increase or decrease of some elements such as As and Sb, followed by the introduction of Ag at the later stage of ore mineral paragenesis sequence. Mineral composition of the Chitose and Koryu deposits are slightly different from those of Shin‐Otoyo, Suttsu, Teine, and Date due to their lack of Sn (tin) and Bi (bismuth) mineralization. The variable concentrations and relationships are not simply with redistributed trace elements from the original sulfide minerals of chalcopyrite, pyrite, galena, and sphalerite. Some heavier elements were also introduced during the replacement reaction, which is consistent with the occurrence of their associated minerals.     

黄沙坪铅锌矿床中银矿化组合特征

研究黄沙坪铅锌矿床中银矿化组合表明：与３０１花岗斑岩和３０４花斑岩岩体有关铅（锌）－银－锡－锑矿化组合，银矿化伴随铅矿化出现，其微量元素富Ｓｎ、Ｓｂ、Ａｇ，低Ｂｉ、Ｔｅ、Ｍｏ、Ｗｏ、Ｗ为特征；银矿物组合以硫银锡矿－银黄锡矿－深红银矿－螺状硫银矿－硫锑铜银矿组合为特征，与石英斑岩有关的铜（钼）－银－碲矿化组合，铜矿石以高Ｔｅ、Ｂｉ、Ｍｏ和Ｗ，低Ｓｂ为特征，银矿物组合以碲银矿－六方碲银矿－粒碲银组合和硫银铋矿－块辉铋铅银矿－碲银矿组合为特征     

Mineralogy and textural relationships among sulphosalts and related minerals in the Bleikvassli Zn-Pb-(Cu) deposit, Nordland, Norway

Several distinct assemblages of Pb-Sb, Pb-As, Cu-Pb-Sb and Cu-Fe-Zn-Sn sulphosalts are identified in sulphide samples from Bleikvassli mine, Norway. Detailed optical microscopy and electron probe microanalysis have permitted investigation of textural relationships between minerals and compositional variations between different ore types. Tetrahedrite, typically containing 10–16?wt.% Ag (rare freibergite containing 25–30?wt.% Ag has also been identified in two samples), stannite (Cu₂(Fe>Zn)SnS₄), and meneghinite, CuPb₁₃Sb₇S₂₄, are widely distributed as trace constituents throughout massive pyritic and galena-rich ores. Native antimony and pyrargyrite occur in trace amounts in all ore types, as the breakdown products of earlier sulphosalts. Several distinct types of wall-rock mineralisation are present at Bleikvassli. Of considerable mineralogical interest are the coarse-grained sulphide mobilisates within the wall rock which contain a distinct?and characteristic suite of Pb-As sulphosalts:?tennantite?+?jordanite (Pb₁₄As₆S₂₃)?+?seligmannite (CuPbAsS₃) ± dufrenoysite (Pb₂As₂S₅). Bournonite (CuPbSbS₃) is the only Sb-bearing sulphosalt recognised in significant amounts within the mobilisates, meneghinite and tetrahedrite being conspicuously absent. These mobilisates display considerable Au enrichment; electrum can be confirmed, intimately associated with jordanite and tennantite. Appreciable Sb (up to 3?wt.%) is contained within galena in the mobilisates, in contrast to galena from massive ores which contains only negligible Sb. Contents of Ag and Bi in galena vary considerably in all ore types, but confirm earlier suggestions that galena is a major Ag-carrier at Bleikvassli. Boulangerite (Pb₅Sb₄S₁₁), jamesonite (FePb₄Sb₆S₁₄) and gudmundite (FeSbS) occur in trace amounts. Sn-sulphosalts are represented by kësterite, (Cu₂(Zn> Fe)SnS₄), but commonly zoned with respect to Zn/Fe ratio, in the mobilisates, rather than by stannite. A rare type of mobilisate, also in the wall rock, in which chalcocite and bornite are the main minerals, contains native Ag, stromeyerite (AgCuS), mckinstryite ((Ag,Cu)₂?S), Ag-free tetrahedrite, an unnamed Cu-Ag-Fe sulphide (Cu₃Ag₂FeS₄) and native Bi, myrmekitically intergrown with chalcocite. Although a comprehensive genetic model for the wall-rock mineralisation at Bleikvassli is largely impossible given the limitations in the present state of knowledge regarding mechanisms involved in remobilisation processes, a multi-stage model of remobilisation during regional metamorphism is considered to best explain the observations. An interplay of different solid- and liquid-state remobilisation mechanisms, in various combinations, is required to account for the macro- and microscopic observations. Remobilisation probably began during the earlier stages of metamorphism, with crystallisation and further remobilisation taking place during the entire metamorphic cycle, giving rise to the extensive chemical and mineralogical diversity observed today. Preserved mineral assemblages and their textural relationships reflect a complex sequence of replacement and decomposition reactions taking place during the latest phase of late-metamorphic crystallisation and subsequent cooling.     

Noble-metal ore genesis and mantle–crust interaction

The mineral and geochemical compositions of noble-metal (first of all, gold) deposits of the Fennoscandian, Siberian, and Northeast Asian orogenic belts are considered. These deposits are of several types: Au (disseminated Au–sulfide and Au–quartz), Au–Bi, Au–Ag, Au–Sb, Ag–Sb, Au–Sb–Hg, and Ag–Hg. They formed in different geodynamic settings as a result of the active motion of crustal tectonic blocks of different nature. Subduction processes (both at the front and at the rear of continent-marginal and island-arc magmatic arcs) resulted in Au–Ag, Ag–Sb, Ag–Hg, Au–Sb–Hg, and Au–Bi deposits. Collision events gave rise to Au and Au–Bi deposits. Intraplate continental rifting and formation of orogenic belts along the boundaries of block (plate) sliding led to the origin of Au and Au–Bi ores in association with Au–Ag, Au–Sb–Hg, and complex ores. In all cases, the formation of noble-metal mineralization was accompanied by magmatism of different types and metamorphism. Because of this diversity of ores, there is no single concept of the genesis of noble-metal mineralization. Several competing models of genesis exist: hydrothermal-metamorphic, pluton-metamorphic, plutonic, activity of mantle fluid flows, and multistage concentration during the crust–mantle interaction with the leading role of sedimentary complexes.     

Minor elements and ore genesis of the Fankou lead-zinc deposit,China

The Fankou Pb-Zn deposit occurs in the Middle-Upper Devonian and Lower Carboniferous carbonate and argillaceous carbonate formations. In principle, the deposit can be classified as a carbonate-hosted strate-bound deposit. Representative sphalerite, galena, and pyrite separates from Fankou have been analysed. For the purpose of comparison a literature survey on minor elements of other districts have been carried out. The comparison of determined data with the quoted data shows that the Fankou sphalerites are rich in Ga, Ge and Ag, but poor in Se and Te; the Fankou galenas are rich in Ag, Hg, Sb and As, but poor in Se, Te, Tl and Bi; the Fankou pyrites are rich in As, Cd and In, but poor in Se, Te, Co and Ni. Zn/Cd and Se/S×10^–4 ratios for sphalerites, Sb/Ag, Sb/Bi and Se/S×10^–4 ratios for galenas and Co/Ni ratios for pyrites from Fankou and other districts have been calculated. Ga-Ge-Ag atomic ratios in sphalerites, Sb-Bi-Ag atomic ratios in galenas and Co-Ni relations in pyrites have been plotted. The average value (311) of Zn/Cd ratios for sphalerites from Fankou is similar to values of sphalerites from Gaobanhe, Heqing, Accesa and Broken Hill. The average Sb/Ag ratio (0.74) and the Sb-Bi-Ag atomic ratios in Fankou galenas are similar to those in the syngenetic galena from the British Island. The Ga-Ge-Ag atomic ratios for Fankou sphalerites are similar to those for the syngenetic sphalerites and Gorno sphalerites. The average Co/Ni ratio (1.1) for micro to fine-grained pyrites from Fankou laminated-bedded pyrite ore is similar to that (0.8) for the sedimentary pyrites from other districts. As to the fine to medium-grained pyrites from Fankou massive pyritic ores, their higher Co/Ni ratios (1.6–1.8) may relate to the fact that more Ni is lost than Co, during the reformation or recrystallization. Sphalerite, galena and pyrite from Fankou all are rather poor in Se and have very low values of Se/S×10^–4, so they may bear no genetic relation to volcanism. To sum up, the following conclusions can be reached: (1) The Fankou deposit possesses some syngenetic features. (2) Evidently it differs from skarn type, hydrothermal type, and volcanogenic type deposits. (3) Surely it is a reformed sedimentary Pb-Zn deposit.     

夏塞银多金属矿床中硫化物和硫盐系列矿物特征及其意义

夏塞矿主档是大型的热液脉型银多金属矿床,通过对大量矿石光（薄）片观察和电子探针分析表明,除主要（方铅矿、富铁闪锌矿）和次要（黄铁矿、毒砂、磁黄铁矿、黄铜矿等）硫化物外,硫盐毓硫物十分发育,主要有Ｃｕ－Ｓｂ－Ａｇ硫盐（黝铜矿、含银黝铜矿和银黝铜矿）、Ｓｂ－Ａｇ硫盐（深红银矿、辉锑银矿）、Ｐｂ－Ｓｂ硫盐（脆硫锑铅矿、硫锑铅矿）和Ｂｉ－Ｐｂ硫盐（斜方辉饿铅矿）。此外,尚有少（微）量黄锡矿、锡石、自然饿和银金矿等。银的硫盐硫物和硫化物（辉银矿）乃是获得银的主要工业矿物,这些硫盐毓矿物常与硫化物伴生,多沿方铅矿、富铁闪锌矿、黄铁矿等的解理、裂隙或粒间产出,这些研究结果不仅有助于了解矿化作用过程,而且为矿床评价,组分综合利用和选冶提供重要依据。     

银多金属矿床中黝铜矿族银硫盐矿物的特征及其意义

在国内外几个不同成因类型的银多金属矿床内产出的黝铜矿族银硫盐矿物中,除朗达矿床见有砷黝铜矿和含银砷黝铜矿外,较普遍共同发育有黝铜矿、含银黝铜矿和银黝铜矿、而后两者是最主要或主要的工业银矿物之一。按国际矿物学协会新矿物及矿物命名委员会的矿物命名原则,黝铜矿族矿物所含的Ｆｅ、Ｚｎ、Ｈｇ、Ｃｄ、Ｍｎ等不可作为矿物种的命名元素。蔡家营矿床的含银黝铜矿和银黝铜矿以Ｆｅ、Ｚｎ含量近似而有别于其余矿床的富Ｆｅ贫     

四川石棉西部碳酸盐岩中金矿床的地质特征和控矿规律

四川石棉西部碳酸盐岩中的金矿床产于泥盆系中统,受层间蚀变破碎带控制。围岩蚀变类型有硅化、碳酸盐化和绢云母化。矿石矿物组分为黄铁矿、黝铜矿、黄铜矿、方铅矿、闪锌矿和Ａｕ－Ａｇ系列矿物,具Ａｕ－Ｃｕ－Ａｇ－Ｐｂ－ＳＡｓ－Ｓｂ－Ｂｉ的元素组合,并一定的垂直分带规律。其成因类型为地下热卤水型。矿床受地层、岩性和断裂的控制明显。并阐明了金矿床的成矿过程和勘查准则。     

Distribution Patterns of Ag in Hydrothermal Precipitates from the Okinawa Trough

The Okinawa Trough is characterized by enrichment of Ag in hydrothermal precipitates; however, the distribution of this enrichment remains poorly constrained. This study presents the results of a field-emission scanning electron microscopy and electron-microprobe analysis based mineralogical and geochemical investigation of the spatial distribution of Ag within Ag-rich sulfide samples from the Okinawa Trough. The tetrahedrite, covellite, and galena in these samples contain high concentrations of Ag(average values of 1.60, 0.78, and 0.23 wt%, respectively) and also various Ag sulfosalts. Examination of the Ag budget of these samples indicates that most of the Ag is hosted by tetrahedrite followed by galena. The Ag within tetrahedrite is incorporated by substitution into the Cu site, whereas galena becomes Ag-enriched by the coupled incorporation of monovalent Ag, Tl, and Cu, and trivalent Sb and Bi into Pb lattice sites. Tetrahedrite and galena containing higher concentrations of Sb favor increased Ag substitution. Four sets of Ag host minerals are identified with distinct ore formation temperatures. Tetrahedrite and galena concentrate the majority of Ag at medium temperatures(150–300°C). Other Ag host minerals concentrate only minor or trace amounts of Ag, including massive sphalerite, chalcopyrite, and pyrite at high temperatures(300°C), colloform pyrite and sphalerite at low temperatures(150°C), and Ag-sulfosalts at even lower temperatures(100°C).     

Trace metal nanoparticles in pyrite

Hydrothermal pyrite contains significant amounts of minor and trace elements including As, Pb, Sb, Bi, Cu, Co, Ni, Zn, Au, Ag, Se and Te, which can be incorporated into nanoparticles (NPs). NP-bearing pyrite is most common in hydrothermal ore deposits that contain a wide range of trace elements, especially deposits that formed at low temperatures. In this study, we have characterized the chemical composition and structure of these NPs and their host pyrite with high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), analytical electron microscopy (AEM), and electron microprobe analysis (EMPA). Pyrite containing the NPs comes from two types of common low-temperature deposits, Carlin-type (Lone Tree, Screamer, Deep Star (Nevada, USA)), and epithermal (Pueblo Viejo (Dominican Republic) and Porgera (Papua New-Guinea)).EMPA analyses of the pyrite show maximum concentrations of As (11.2), Ni (3.04), Cu (2.99), Sb (2.24), Pb (0.99), Co (0.58), Se (0.2), Au (0.19), Hg (0.19), Ag (0.16), Zn (0.04), and Te (0.04) (in wt.%). Three types of pyrite have been investigated: “pure” or “barren” pyrite, Cu-rich pyrite and As-rich pyrite. Arsenic in pyrite from Carlin-type deposits and the Porgera epithermal deposit is negatively correlated with S, whereas some (colloform) pyrite from Pueblo Viejo shows a negative correlation between As + Cu and Fe. HRTEM observations and SAED patterns confirm that almost all NPs are crystalline and that their size varies from 5 to 100 nm (except for NPs of galena, which have diameters of up to 500 nm). NPs can be divided into three groups on the basis of their chemical composition: (i) native metals: Au, Ag, Ag–Au (electrum); (ii) sulfides and sulfosalts: PbS (galena), HgS (cinnabar), Pb–Sb–S, Ag–Pb–S, Pb–Ag–Sb–S, Pb–Sb–Bi–Ag–Te–S, Pb–Te–Sb–Au–Ag–Bi–S, Cu–Fe–S NPs, and Au–Ag–As–Ni–S; and (iii) Fe-bearing NPs: Fe–As–Ag–Ni–S, Fe–As–Sb–Pb–Ni–Au–S, all of which are in a matrix of distorted and polycrystalline pyrite. TEM-EDX spectra collected from the NPs and pyrite matrix document preferential partitioning of trace metals including Pb, Bi, Sb, Au, Ag, Ni, Te, and As into the NPs. The NPs formed due to exsolution from the pyrite matrix, most commonly for NPs less than 10 nm in size, and direct precipitation from the hydrothermal fluid and deposition into the growing pyrite, most commonly for those > 20 nm in size. NPs containing numerous heavy metals are likely to be found in pyrite and/or other sulfides in various hydrothermal, diagenetic and groundwater systems dominated by reducing conditions.     

蒙古国那仁陶勒盖金矿床原生晕特征及深部预测

为预测和评价那仁陶勒盖金矿的成矿潜力,运用多元统计方法,结合地球化学各参数信息,对那仁陶勒盖金矿原生晕进行系统研究.结果显示:那仁陶勒盖金矿赋矿花岗闪长岩中Au、Ag、Bi等元素浓集克拉克值明显偏高,与那仁陶勒盖金成矿作用关系密切;矿石中Au与Sb、Cu、Pb、Ag、Hg、Zn、As、Bi等关系最为密切;矿体原生晕轴向分带序列出现尾晕元素W、Sn等与前缘晕元素As叠加的现象,同时(As+Sb)/(Bi+Mo)、100Sb/(Bi·Mo)等分带性指数出现转折,指示深部存在盲矿体.依据上述矿体原生晕特征,建立矿体叠加晕预测模型,预测盲矿体赋存位置在海拔710m以下的岩体与地层接触带附近.     

招远大尹格庄金矿床微量元素特征及其意义

该文以山东招远大尹格庄金矿床中微量元素为研究对象,通过对矿床围岩、矿石等微量元素的研究,表明大尹格庄金矿围岩中微量元素以富含 Bi,Au,Pb,W,Ag,Sn 为特点,矿体和矿化体中元素组合为 Au,Ag,As,Sb,Hg,B, Cu,Zn,Bi,Mo,Mn,Co,Ni,W。在5个成矿阶段中,第二阶段与第三阶段微量元素的富集程度较明显,表现为 Au, Ag,As,Co,Bi,Cu,Pb,Zn 等的富集,成矿元素可分为2个分带序列,主成矿元素为 Au Ag Cu Pb Zn Bi 组合、头晕元素 As Sb Hg 组合和尾晕元素 Co Ni 组合。