Discordant iron-rich ultramafic pegmatites (IRUPs) intersect the UG2 chromitite at many places in the Bushveld Complex. The effects of IRUP interactions on the UG2 ore mineralogy and PGE grade are assessed at the Thaba mine, north-west Bushveld, based on a borehole profile through the UG2 layer and detailed analysis of mineral textures and compositional variations across the UG2-IRUP contacts using micro-XRF element mapping. The UG2-IRUP interaction operated at different scales and probably by different mechanisms. At the local scale (< 10 cm), a thin layer of Fe–Ti–Cr spinel and ilmenite formed on the IRUP side of the contact with UG2, whereas the UG2 chromitite developed grain coarsening, loss of interstitial silicates, and chemical gradients in Cr, Al, Fe, and Ti that extend a few centimeters from the contact into the seam. These local effects are attributed to the intrusion of IRUP melt into the solidified UG2 layer, followed by re-equilibration of the oxide minerals across the contact during cooling. On a larger scale, changes in the ore and gangue mineral assemblages in UG2 took place throughout the entire meter-thick main seam. Compared with regional UG2 compositions, chromite has higher TiO₂ and lower Mg#, and there is an anomalously low abundance of interstitial plagioclase. The IRUP-affected UG2 shows relatively abundant secondary hydrous silicates, replacement of PGE sulfides by PGE alloys and PGE-As–Sb–Bi–Te–Pb phases, and formation of secondary Ni–Cu–Fe sulfides after pentlandite and chalcopyrite. These large-scale effects are attributed to hydrothermal fluids derived from IRUP melts. The IRUP bodies at the Thaba mine caused redistribution of PGE within the UG2 layer but did not significantly reduce the overall grade. However, significant changes in the ore mineral assemblage and an increased abundance of secondary silicates can reduce the efficiency of PGE recovery.

不协调的富铁超镁铁伟晶岩 (IRUP) 在 Bushveld Complex 的许多地方与 UG2 铬铁矿相交。IRUP 相互作用对 UG2 矿石矿物学和 PGE 品位的影响在布什维尔德西北部的 Thaba 矿进行了评估，该评估基于通过 UG2 层的钻孔剖面以及使用 UG2-IRUP 接触面的矿物结构和成分变化的详细分析微型 XRF 元素映射。UG2-IRUP 交互在不同的规模上运行，可能通过不同的机制运行。在局部尺度（< 10 cm），在与 UG2 接触的 IRUP 侧形成了一层薄薄的 Fe-Ti-Cr 尖晶石和钛铁矿，而 UG2 铬铁矿则出现晶粒粗化、间隙硅酸盐损失和化学梯度Cr、Al、Fe 和 Ti 从触点延伸到接缝中几厘米。这些局部效应归因于 IRUP 熔体侵入凝固的 UG2 层，随后在冷却过程中通过接触重新平衡氧化物矿物。在更大范围内，UG2 的矿石和脉石矿物组合的变化发生在整个米厚的主煤层。与区域 UG2 成分相比，铬铁矿具有更高的 TiO₂和较低的 Mg#，间隙斜长石的丰度异常低。受 IRUP 影响的 UG2 显示出相对丰富的次生水合硅酸盐，PGE 合金和 PGE-As-Sb-Bi-Te-Pb 相替代 PGE 硫化物，并在镍黄铁矿和黄铜矿之后形成次生 Ni-Cu-Fe 硫化物。这些大规模效应归因于源自 IRUP 熔体的热液流体。Thaba 矿的 IRUP 体导致 PGE 在 UG2 层内重新分布，但并未显着降低整体品位。然而，矿石矿物组合的显着变化和次生硅酸盐丰度的增加会降低 PGE 的回收效率。