The Jabali nonsulfide Zn–Pb–Ag deposit, western Yemen
The Jabali nonsulfide Zn–Pb–Ag deposit, western Yemen
复制标题
DOI：
10.1016/j.oregeorev.2014.02.003
复制
发表时间：
2014-09
影响因子：
3.3
通讯作者：
N. Mondillo;M. Boni;G. Balassone;M. Joachimski;A. Mormone
中科院分区：
文献类型：
--
作者：
N. Mondillo;M. Boni;G. Balassone;M. Joachimski;A. Mormone
Jabali锌铅银存款位于也门首都萨那以东约110公里处，沿着Marib-Al-Jawf/Sab'atayn盆地的西部边界。Jabali的经济矿化是一种非硫化物存款，由870万吨，平均品位为9.2%的锌，来自原生硫化物的氧化。原生矿和次生矿的岩石是侏罗纪Shuqra组（Amran群）的强烈石化的碳酸盐台地石灰岩。原生硫化物由闪锌矿、方铅矿和黄铁矿/白铁矿组成。菱锌矿是次生存款中最丰富的经济矿物，并与少量的水锌矿、异极矿、针铁矿和绿菱锌矿共生。菱锌矿主要有两代：菱锌矿1代，它取代了寄主白云石和闪锌矿;菱锌矿2代，它在寄主岩石中作为结核和脉填充物出现。在菱锌矿1和寄主白云岩之间的边界处，后者被宽的、不规则的含锌白云岩带广泛取代，其中Zn取代了Mg。次生成矿作用经历了不同的阶段：1）原始硫化物（闪锌矿、黄铁矿和方铅矿）的蚀变和金属在酸性溶液中的释放; 2）白云岩寄主岩石的蚀变和含锌白云岩的形成; 3）白云岩被含金属的酸性流体部分溶解并被第一个菱锌矿相（菱锌矿1）取代。次生矿物对闪锌矿和方铅矿的直接交代作用也属于这一阶段（菱锌矿和白铅矿）; 4）后期菱锌矿相的沉淀（菱锌矿2）的δ ~（18）O组成一般低于已知的表生菱锌矿，而碳同位素组成与大多数表生非硫化物矿石中记录的负δ 13 C值范围相同。考虑到也门这一地区的地下沃茨和古地下沃茨具有负δ 18 O值，可以假设Jabali菱锌矿是在不同阶段从流体组合中沉淀出来的，可能由当地地下沃茨和低温热液沃茨混合而成。碳同位素组成被解释为来自寄主岩石碳酸盐的碳与土壤/大气CO2混合的结果。Jabali次生存款发育的最有利背景可以被置于中新世早期（~ 17 Ma），当时表生风化受到红海伸展主阶段导致的主要隆升和剥露的有利影响。低温热液流体也可能在同一时间通过该地区岩浆引发的地热活动循环。
The Jabali Zn–Pb–Ag deposit is located about 110 km east of Sana'a, the capital of Yemen, along the western border of the Marib-Al-Jawf/Sab'atayn basin. The economic mineralization at Jabali is a nonsulfide deposit, consisting of 8.7 million tons at an average grade of 9.2% zinc, derived from the oxidation of primary sulfides. The rock hosting both primary and secondary ores is a strongly dolomitized carbonate platform limestone of the Jurassic Shuqra Formation (Amran Group). The primary sulfides consist of sphalerite, galena and pyrite/marcasite. Smithsonite is the most abundant economic mineral in the secondary deposit, and is associated with minor hydrozincite, hemimorphite, acanthite and greenockite. Smithsonite occurs as two main generations: smithsonite 1, which replaces both host dolomite and sphalerite, and smithsonite 2, occurring as concretions and vein fillings in the host rock. At the boundary between smithsonite 1 and host dolomite, the latter is widely replaced by broad, irregular bands of Zn-bearing dolomite, where Zn has substituted for Mg. The secondary mineralization evolved through different stages: 1) alteration of original sulfides (sphalerite, pyrite and galena), and release of metals in acid solutions; 2) alteration of dolomite host rock and formation of Zn-bearing dolomite; 3) partial dissolution of dolomite by metal-carrying acid fluids and replacement of dolomite and Zn-bearing dolomite by a first smithsonite phase (smithsonite 1). To this stage also belong the direct replacement of sphalerite and galena by secondary minerals (smithsonite and cerussite); 4) precipitation of a later smithsonite phase (smithsonite 2) in veins and cavities, together with Ag- and Cd-sulfides.The δ18O composition of Jabali smithsonite is generally lower than in other known supergene smithsonites, whereas the carbon isotope composition is in the same range of the negative δ13C values recorded in most supergene nonsulfide ores. Considering that the groundwaters and paleo-groundwaters in this area of Yemen have negative δ18O values, it can be assumed that the Jabali smithsonite precipitated in different stages from a combination of fluids, possibly consisting of local groundwaters variably mixed with low-temperature hydrothermal waters. The carbon isotope composition is interpreted as a result of mixing between carbon from host rock carbonates and soil/atmospheric CO2.The most favorable setting for the development of the Jabali secondary deposit could be placed in the early Miocene (~ 17 Ma), when supergene weathering was favored by major uplift and exhumation resulting from the main phase of Red Sea extension. Low-temperature hydrothermal fluids may have also circulated at the same time, through the magmatically-induced geothermal activity in the area.