川南玄武岩晶洞中的沥青与铜矿物球粒研究

Study on the Bitumen and Cu-bearing Mineral Spherulite from Basaltic Druse in South Sichuan

川南普格杏仁状玄武岩晶洞中产出大量石英、水晶、沥青、葡萄石以及铜矿物,根据其产状和矿物组合分为石英-沥青、水晶-沥青及水晶-葡萄石球粒三种类型晶洞。水晶-葡萄石晶洞中矿物组合具明显球粒形貌特点,球粒由中心柱状水晶及垂直水晶柱面生长的葡萄石球粒内圈与铜矿物球粒外圈组成。铜矿物球粒具有明显圈层结构,由自然铜核、黑铜矿幔、硅孔雀石与孔雀石壳组成。野外及镜下观察显示,铜矿物集合体形态受自然铜形状和产出控制,铜矿物球粒主要分布于多个葡萄石球粒边缘的汇聚处,核部自然铜为球粒状;脉状铜矿物由一向伸长自然铜与黑铜矿、硅孔雀石等矿物组成,分布于晶洞裂隙中。碳同位素与红外光谱研究表明晶洞中的沥青为生物成因,属石油沥青,有机质可能来自下二叠统（P1^3）碳酸盐。晶洞中矿物为含有机质成矿溶液依次结晶而成,其顺序为：玉髓或石英→水晶、沥青与自然铜→自然铜与葡萄石→黑铜矿→硅孔雀石→孔雀石→方解石。沥青的螺旋生长花纹特征、水晶中包裹体均一化温度以及水晶中沥青与自然铜之间的关系显示,沥青是有机质（原油）受热裂解转变而成,其形成温度约为290~230℃,自然铜的结晶温度为230~160℃。

Quartz, bitumem, prehnite and Cu-bearing minerals widely occur in amygdaloid basaltic druse from Puge county, southSichuan. According to their occurrences and relationships, three types of basaltic druse are divided： quartz-bitumen druse, rockcrystal-bitumen druse, rock crystal-prehnite druse. The mineral assemblages from rock crystal-prehnite druse display the feature ofnodules, which outward include prismatical rock crystals, prehnite spherulites and Cu-bearing minerals spherulites. Moreover,Cu-bearing minerals spherulites have the feature of circle layered structure, including native copper（core）, tenorite（mantle） andchalcostaktite-malachite（crust）. Observations in field and under microscope show that the shapes and occurrences of native coppercontrol the pattern of the Cu-bearing minerals aggregations. Cu-bearing minerals spherulites are mainly distributed in the convergencesamong the prehnite spherulites, and the core is granular native copper. Cu-bearing minerals veins include stretch native copper,tenorite, chalcostaktite, occur in the fractures of druses. The carbon isotope and infrared spectrum suggest that asphalt is of biogenesisand originated from the carbonate rocks in Permian strata（P1^3）. The minerals in basaltic druses crystallized from the organic fluids, the commonly recognized sequence is chalcedony → quartz ＋ bitumen ＋ native copper → native copper ＋ prehnite → tenorite →chalcostaktite → malachite →calcite. The spiral growth patterns of bitumen, homogenization temperature of inclusions in quartz andthe relationships between bitumen and native copper in rock crystal indicate that bitumen formed under the thermal cracking of organic（crude oil）, the temperature is 290-230℃. Native copper crystallized under 230-160℃.