Gaseous transport and deposition of gold in magmatic fluid: evidence from the active Kudryavy volcano, Kurile Islands

The distribution of gold in high-temperature fumarole gases of the Kudryavy volcano (Kurile Islands) was measured for gas, gas condensate, natural fumarolic sublimates, and precipitates in silica tubes from vents with outlet temperatures ranging from 380 to 870°C. Gold abundance in condensates ranges from 0.3 to 2.4 ppb, which is significantly lower than the abundances of transition metals. Gold contents in zoned precipitates from silica tubes increase gradually with a decrease in temperature to a maximum of 8 ppm in the oxychloride zone at a temperature of approximately 300°C. Total Au content in moderate-temperature sulfide and oxychloride zones is mainly a result of Au inclusions in the abundant Fe–Cu and Zn sulfide minerals as determined by instrumental neutron activation analysis. Most Au occurs as a Cu–Au–Ag triple alloy. Single grains of native gold and binary Au–Ag alloys were also identified among sublimates, but aggregates and crystals of Cu–Au–Ag alloy were found in all fumarolic fields, both in silica tube precipitates and in natural fumarolic crusts. Although the Au triple alloy is homogeneous on the scale of microns and has a composition close to (Cu,Ni,Zn)₃(Au,Ag)₂, transmission electron microscopy (TEM) shows that these alloy solid solutions consist of monocrystal domains of Au–Ag, Au–Cu, and possibly Cu₂O. Gold occurs in oxide assemblages due to the decomposition of its halogenide complexes under high-temperature conditions (650–870°C). In lower temperature zones (<650°C), Au behavior is related to sulfur compounds whose evolution is strongly controlled by redox state. Other minerals that formed from gas transport and precipitation at Kudryavy volcano include garnet, aegirine, diopside, magnetite, anhydrite, molybdenite, multivalent molybdenum oxides (molybdite, tugarinovite, and ilsemannite), powellite, scheelite, wolframite, Na–K chlorides, pyrrhotite, wurtzite, greenockite, pyrite, galena, cubanite, rare native metals (including Fe, Cr, Mo, Sn, Ag, and Al), Cu–Zn–Fe–In sulfides, In-bearing Pb–Bi sulfosalts, cannizzarite, rheniite, cadmoindite, and kudriavite. Although most of these minerals are fine-grained, they are strongly idiomorphic with textures such as gas channels and lamellar, banded, skeletal, and dendrite-like crystals, characteristic of precipitation from a gas phase. The identified textures and mineral assemblages at Kudryavy volcano can be used to interpret geochemical origins of both ancient and modern ore deposits, particularly gold-rich porphyry and related epithermal systems.     

新桥硫铁矿伴生金银赋存状态及分布规律

系统阐述了新桥矿伴生金银的赋存状态和分布规律 ,对综合利用矿产资源 ,提高金银的回收率 ,以及深部资源预测、外围找矿均具有一定的指导意义     

Geochemical Characteristics of Volcanic Rocks of the Laochang Ag Polymetallic Deposit,Lancang,Yunnan Province,China

In terms of major element, trace element and REE geochemical characteristics ofvolcanic rocks in the area studied and by making use of the TiO2-K2O-P2O5,The-Hf-Ta and Zr-Nb-Y trianglar diagrams and the environmental discrimination diagrams of incompatible ele-ment distribution pattems,the authors have drawn some conclusions that are different from those by previous workers.It is concluded that volcanic rocks in the Laochang Ag polymetallic deposit at Lancang,Yunnan belong to continental within-plate alkali basalts, and that their geotectonic setting seems to be at the northeastern margin of East Gondwana Land.     

粤桂边境庞西垌—金山银金矿床特征与成因

庞西垌—金山银金矿床位于广东廉江县与广西博白县的交界,是一个以银为主,含有金、铅、锌等伴生有益组分的银多金属矿床。地质地球化学研究结果表明,该矿床是中低温蚀变构造岩型银金矿床。矿床的成矿物质主要来源于前寒武系—寒武系变质岩系,燕山期英桥花岗岩浆活动提供了热源,驱使以大气降水为主含有岩浆热液的混合水循环并对围岩进行淋滤,形成成矿溶液体系;成矿溶液沿多期次活动的庞西垌—金山断裂带运移,在运移过程中与围岩发生蚀变作用,矿床最后定位,矿化与硅化、绢云母化、黄铁矿化关系密切。     

浙江中生代浅成热液金银成矿系统的自组织与耗散结构

浙江中生代浅成热液金银矿床多具明显的热液蚀变 (矿化 )分带—自组织结构。通过对围岩蚀变—矿化过程中的W /R(水 /岩 )比值、元素的带出 (λ)量[EO(I)A] ,熵变 (ΔS)、成矿成岩时差(Δti)和S°298/di(标准熵 /离子密度 )比值、盐度 (St)、P(压力 )、fs2(硫逸度 )和fo2(氧逸度 )、δ18OH2O 和δD、206Pb/204Pb和207Pb/204Pb值等变化的研究 ,表明浅成热液金银成矿系统是一个非平衡 (距热力学平衡态有一定距离 )的开放系统 ,矿床都是在开放环境下成矿流体通过能量的不断耗散并与围岩发生物质交换的一种自组织过程中形成的 ,具耗散结构的特征。一般W/R、EO(I)A和Δti与S°298/di∝MSOD(成矿系统开放程度 )。也就是说 ,围岩蚀变 -矿化过程中W /R比值、元素的带出(入 )量和Δti与S°298/di比值及ΔS值较大 ,一般成矿系统的开放程度也较高 ,成矿一般也较有利     

发射光谱法定量测定岩矿、土壤中的Ag、B、Sn、Mo

样品以焦硫酸钾、氟化钠、三氧化二铝和碳粉为缓冲剂,改善各元素的蒸发行为,采用较短的摄谱时间,大大降低光谱背景,以两根装样电极两次重叠摄谱,分别对长波、短波相板采用不同显影时间,以锗作为内标元素,实现了试样中银、硼、锡、钼的同时定量测定.方法应用于岩石、土壤等地质样品测试中取得了满意的结果。     

闽中地区次火山-热液金（银）矿床成矿系列及资源潜力

闽中地区是福建省金银成矿集中区,其上规模成矿主要集中于晚侏罗世次火山活动阶段。次火山-热液金(银)矿床的形成,矿、热、水“三源”是基本必要条件,北西、北东向两组构造带的复合是成矿定位的关键。在断隆带、坳中隆、坳中凹不同构造环境中,相应地递次形成(次)辉绿岩-闪长玢岩、(次)英安斑岩、(次)流纹斑岩等区域次火山-热液金(银)矿床成矿系列的3个亚系列;在垂向空间分布上,自上而下构成(微)细粒浸染型、石英脉型、破碎带蚀变岩型、隐爆角砾岩型、次火山岩型等工业矿床类型分带序列。金矿资源潜力在50t以上。     

冀北含银岩石建造、区域地球化学特征及成矿预测

从构造地质位置、岩石类型、岩石学、岩石化学、含银丰度、区域展布等方面,确定了冀北存在有３种含银岩石建造类型（１．古元古代含银变质岩建造;２．中元古代高于庄期含银碳酸盐岩建造;３．中生代晚侏罗世张家口期含银火山岩建造）。基于各含银岩石建造内Ａｇ,Ａｕ,Ｃｕ,Ｐｂ,Ｚｎ,Ｍｎ,Ｗ,Ｎｉ,Ｓｎ,Ｃｒ,Ｂ,Ｔｉ,Ｖ,Ｍｏ,Ｃｏ等１５个元素的化学定量分析,Ｒ型聚类分析、因子分析和相关矩阵分析,明确了冀北含银     

半叶马尾藻对N、P吸收速率的初步研究

在实验室条件下研究半叶马尾藻对不同浓度N、P以及不同化合态N的吸收速率。结果显示:不同浓度N、P下,半叶马尾藻对N、P的吸收速率差异有统计学意义(P0.05);半叶马尾藻对N、P的吸收速率随N、P浓度的升高而增加,最大吸收速率出现在N为200μmol/L、P为20μmol/L时,分别为2.397和0.229μmol·g-1·h-1;不同氮磷比条件下,半叶马尾藻对N、P的最大吸收速率出现在氮磷比为10时,在氮磷比为1~30范围内,氮磷比对半叶马尾藻吸收N、P速率的影响有统计学意义(P0.05);不同化合态N对半叶马尾藻吸收N、P速率的影响有统计学意义(P0.05),当NH4+-N和NO3--N共存时,半叶马尾藻对这2种化合态氮可同时吸收利用,各处理组间,对总无机N的吸收速率差异有统计学意义(P0.05),在c(NO3--N)/c(NH4+-N)为2∶1和1∶2处有两个峰值,分别为2.036、1.862μmol·g-1·h-1,对P的最大吸收速率均出现在c(NO3--N)/c(NH4+-N)值为2∶1时,为0.206μmol·g-1·h-1。因此,在粤西沿海半叶马尾藻在消除养殖水域营养盐、防治海水富营养化方面有很大优势。     

GFAAS法测定地质样品中痕量银

采用石墨炉原子吸收光谱法测定化探样品中痕量银。选择仪器最佳温度程序,采用四酸溶样,硝酸介质,硫脲、铱盐为基体改进剂,国家一级标准样品绘制工作曲线。在取样0．1000g,定容10mL情况下,方法检出限为0．01ug／g,经用国家标准物质验证,测定准确度和精密度比较满意。