Chang Jia, Audétat Andreas, Pettke Thomas
Bavarian Geoinstitute, University of Bayreuth, Bayreuth, Germany.
State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan, China.
Nat Commun. 2025 Mar 8;16(1):2330. doi: 10.1038/s41467-025-57710-z.
Porphyry-type Cu (Mo, Au) deposits are among the economically most important ore resources. The depth and mode of ore-forming fluid exsolution from their source magmas has remained poorly constrained. Here, we studied 36 magmatic rocks from six mineralized systems in the Sanjiang region of southwestern China. Melt inclusions trapped in the phenocrysts of mineralizing, felsic magmas are strongly depleted in Cl, S, and metals. Petrographic evidence, apatite volatile contents, and mass balance calculations suggest that this depletion was caused by the exsolution of aqueous fluids, which extracted 63‒97% of the Cl, S, and metals originally present in the magmas. Three independent geobarometers reveal that all the major phenocrysts in the felsic magmas crystallized within the pressure range of 0.3‒0.5 GPa. These results show that the ore-forming fluids exsolved from magmas that crystallized at mid- to upper crustal depths of ~10‒20 km, rather than from magmas crystallizing entirely within the upper crust or from magmas directly ascending from the lower crust. The fluids thus had to transport their metal and S endowments over a vertical distance of ~10 km to the site of ore precipitation, likely first via bubbles suspended in ascending porphyry magmas, and then through an interconnected fluid network.
斑岩型铜（钼、金）矿床是经济上最重要的矿石资源之一。其成矿流体从源岩浆中出溶的深度和方式一直缺乏明确的限制。在此，我们研究了中国西南部三江地区六个矿化系统中的36块岩浆岩。矿化长英质岩浆斑晶中捕获的熔体包裹体在氯、硫和金属方面严重亏损。岩石学证据、磷灰石挥发物含量和质量平衡计算表明，这种亏损是由水流体的出溶造成的，水流体提取了岩浆中原本存在的63%-97%的氯、硫和金属。三种独立的地质压力计显示，长英质岩浆中的所有主要斑晶均在0.3-0.5GPa的压力范围内结晶。这些结果表明，成矿流体是从在约10-20km的中上地壳深度结晶的岩浆中出溶的，而不是从完全在上地壳中结晶的岩浆或直接从下地壳上升的岩浆中出溶的。因此，这些流体必须将其金属和硫的含量垂直输送约10km到矿石沉淀地点，可能首先通过悬浮在上升斑岩岩浆中的气泡，然后通过相互连接的流体网络。
