楚雄盆地六苴砂岩型铜矿床成矿流体性质及演化

六苴铜矿床是中国南方中、新生代红层盆地中典型的陆相砂岩型铜矿床,具有明显的"金属矿物分带"及"浅色和紫色砂岩过渡带控矿"两大特征。为探讨该矿床流体演化及成矿机制,本文以矿化类型及成矿期次划分为基础,进行了详细的流体包裹体特征、显微测温及成分分析研究。研究结果表明,六苴铜矿床成矿作用主要经历成岩期和改造期两个时期,改造期分早、晚两阶段。两期次的流体包裹体均以纯液相型和富液型盐水包裹体为主,流体均一温度具有先升高后降低的演化趋势,温度范围分别为:96~164℃、108~227℃、94~159℃;而盐度(w(NaCl))差别不大,改造期比成岩期略低,范围分别为2.7%~16.7%、2.1%~13.8%、1.2%~13.5%,总体属中低温—中低盐度盆地卤水。包裹体岩相学观察与激光拉曼气相成分测试表明,成岩期含少量烃类包裹体,而改造期含少量CO_2包裹体。两期包裹体群体成分也有一定差异:挥发分具有从还原性富有机质的CH_4端元向相对氧化的CO_2端元演化的特点;离子成分由富SO_4~(2-)(-Cl-)-Ca~(2+)-K+型向富Cl~--Na~+型转变。成岩期流体演化形成了砂岩铜矿层状产出的浸染状或纹层状矿(化)体,改造期的构造流体在层状矿(化)体基础上进一步演化形成受构造控制的条带状、脉状富矿体(脉)。

Properties and Evolution of Ore-Forming Fluid in Liuju Sandstone Type Copper Deposit,Chuxiong Basin in Yunnan Province

Liuju copper deposit is one of the typical terrestrial sandstone‐type deposits ,and w hich is located in the Meso‐Cenozoic red‐bed basin of South China .The mineralization occurred in the interface between the purple and grey beds of medium‐fine grained sandstone strata . Besides , Hematite , chalcocite ,bornite ,chalcopyrite ,and pyrite coexist in this transitional zone from the purple bed to grey bed ,a horizontal metallic mineral zone .Aiming at the ore‐forming fluid evolution and mineralization mechanism ,this paper focuses on the characteristics of fluid inclusions on the basis of mineralization types and mineralizing periods .The fluid mineralization of Liuju deposit can be divided into diagenesis period and tectonic‐reworked period ;the latter can be further divided into early and late stages .In the two stages , fluid inclusions are predominated by pure‐liquid type aqueous inclusions and gas‐liquid aqueous inclusions with rich liquid .The homogenization temperatures of the three stages experienced an evolution trend as follow s :increased from 96 164 ℃ to 108 227 ℃ ,then decreased to 94 159 ℃ ;while the salinities (w (NaCl)) were slightly decreased from 2 .7% 16 .7% to 2 .1% 13 .8% ,then 1 .2% 13 .5% ,showing little difference .Generally ,all the three stages of the ore‐forming fluid were medium‐low temperature and medium‐low salinity basin brine .By the petrographic feature observation and the laser raman spectroscopy test of the gas component in fluid inclusions ,it was confirmed that small amounts of hydrocarbon fluid inclusions were contained in the diagenesis period ;while small amounts of three‐phase CO2 inclusions were found in the tectonic‐reworked period . Besides , their grouped fluid compositions are different .The ore‐forming fluid experienced a trend as follows :the gas component changed from the reducing organic‐rich end (CH4 ) to the relatively oxidizing end (CO2 ) in the N2 CH4 CO2 triangular diagram ;meanwhile ,the ionic component changed from the rich SO2 -4 (-Cl-) Ca2+ K+ type to the rich Cl- Na+ type .Different properties of ore‐forming fluids played different roles in the mineralization of bedded orebodies and veined orebodies .During the ore‐forming fluid evolution ,the disseminated or laminated ores in sandstone‐type copper deposits were formed in the diagenesis period ;w hile ,the high‐grade banded ,veined ores on the base of bedded orebody controlled by the fracture are formed during the further evolution in tectonic‐reworked period .