The copper-nickel(-platinum-group element) sulfide resources of the Duluth Complex, Minnesota, USA, formed by assimilation of sulfur from the Virginia Formation black shale. In the normal black shale of the Virginia Formation, sulfur is mainly hosted in disseminated pyrite, whereas mm-scale pyrrhotite laminae dominate in the sulfur-rich Bedded Pyrrhotite Unit. The Bedded Pyrrhotite Unit was the main supply of sulfur in some of the magmatic sulfide deposits but its origin has not been studied in detail. Using Raman spectroscopy, we show that the carbonaceous material within the regionally metamorphosed normal black shale is graphitized biogenic material. The Bedded Pyrrhotite Unit contains pyrobitumen that represents residues of oil that accumulated to porous horizons, which formed due to dissolution of precursor sedimentary clasts. Replacement of the clasts by quartz and sulfides facilitated the formation of the pyrrhotite laminae of the Bedded Pyrrhotite Unit, which likely occurred during regional metamorphism.

The pyrite-bearing normal black shale experienced loss of H₂O, C_org, and sulfur during devolatilization caused by the Duluth Complex. The contact-metamorphosed Bedded Pyrrhotite Unit shows no systematic depletion of volatiles and is the most C_org and sulfur-rich part of the Virginia Formation. During devolatilization, sulfur was preserved because unlike pyrite, pyrrhotite was stable. Consequently, magmatic assimilation of sulfur from the Bedded Pyrrhotite Unit required partial melting. Retrograde hydration introduced H₂O, and possibly C_org, and sulfur, to the contact-metamorphosed Bedded Pyrrhotite Unit, which further affected the volatile budget. Our findings highlight why constraining diagenetic and regional metamorphic processes is important to understand magma-sediment interaction processes.

美国明尼苏达州德卢斯复合体的铜镍（铂族元素）硫化物资源，是由弗吉尼亚组黑色页岩中的硫同化形成的。在弗吉尼亚组的正常黑色页岩中，硫主要赋存于浸染状黄铁矿中，而毫米级磁黄铁矿纹层主要存在于富硫层状磁黄铁矿单元中。层状磁黄铁矿单元是一些岩浆硫化物矿床中硫的主要来源，但其来源尚未得到详细研究。使用拉曼光谱，我们表明区域变质的正常黑色页岩中的碳质材料是石墨化的生物成因材料。层状磁黄铁矿单元含有焦沥青，代表石油残留物，这些石油残留物积累到多孔地层，这些石油残留物是由于前体沉积碎屑的溶解而形成的。石英和硫化物取代碎屑促进了层状磁黄铁矿单元磁黄铁矿纹层的形成，这可能发生在区域变质作用期间。

含黄铁矿的正常黑色页岩在德卢斯杂岩引起的脱挥发分过程中经历了H ₂ O、C _org和硫的损失。接触变质层状磁黄铁矿单元没有显示出挥发物的系统性消耗，并且是弗吉尼亚组中最富含_有机质和硫的部分。在脱挥发分过程中，硫被保留下来，因为与黄铁矿不同，磁黄铁矿很稳定。因此，岩浆同化层状磁黄铁矿单元中的硫需要部分熔化。逆行水合作用将H ₂ O、可能的C _org和硫引入到接触变质的层状磁黄铁矿单元中，这进一步影响了挥发性预算。我们的研究结果强调了为什么限制成岩和区域变质过程对于理解岩浆-沉积物相互作用过程很重要。