The origin of PGE-Ni-Cu mineralization in the Platreef, northern limb of the Bushveld Igneous Complex (BIC), and the possible correlation with the Merensky Reef in the eastern and western limbs has been long debated. The Platreef and Merensky Reef share the same stratigraphic position in the uppermost part of the Upper Critical Zone (UCZ), near the transition to the overlaying Main Zone (MZ). However, discrepancies in interpretations have been difficult to resolve due to the effects of intense magma-country rock interaction throughout most of the northern limb succession. To address this problem, we generated a detailed stratigraphic profile of the initial strontium isotopic ratio [Sr i = ( 87 Sr/ 86 Sr) i ] in plagioclase across a Flatreef interval lacking macroscopic evidence of country rock assimilation. The in situ Sr isotopic ratios in plagioclase were determined using LA-MC-ICP-MS analysis on 37 samples from a drill core (UMT094) at the Turfspruit project. Strontium isotope stratigraphy is useful because of a well-documented shift in Sr i near the base of the Merensky Unit in the eastern and western limbs. The results show the existence of a significant shift (from Sr i = 0.7060 to Sr i = 0.7090) that matches the isotopic shift documented through the Merensky Unit in the eastern and western limbs. Thus, this new Sr isotope data indicates that the main mineralized interval of the Flatreef can be stratigraphically correlated to the Merensky Reef in the remainder of the BIC. In addition, we interpret these results as compelling evidence to suggest that the main mineralization processes in the Flatreef were likely similar to those operating in the eastern and western limbs and that interaction with local country rocks was not a necessary condition.

中文翻译：

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布什维尔德火成岩杂岩北缘 Turfspruit 的 Flatreef PGE-Ni-Cu 矿化区的锶同位素地层学：与东缘和西缘梅伦斯基单元相关的证据


布什维尔德火成岩杂岩体 (BIC) 北缘 Platreef 中 PGE-Ni-Cu 矿化的起源，以及与东缘和西缘 Merensky 礁的可能相关性一直存在争议。 Platreef 和 Merensky 礁在上临界区 (UCZ) 的最上部具有相同的地层位置，靠近与覆盖的主区 (MZ) 的过渡。然而，由于北缘序列大部分地区岩浆与岩石相互作用的影响，解释上的差异很难解决。为了解决这个问题，我们在缺乏围岩同化宏观证据的 Flatreef 区间生成了斜长石中初始锶同位素比 [Sr i = ( 87 Sr/ 86 Sr) i ] 的详细地层剖面。使用 LA-MC-ICP-MS 分析来自 Turfspruit 项目钻芯 (UMT094) 的 37 个样品，确定了斜长石中的原位 Sr 同位素比率。锶同位素地层学非常有用，因为在东部和西部边缘梅伦斯基单元底部附近的 Sr i 发生了有据可查的变化。结果表明，存在显着的转变（从 Sr i = 0.7060 到 Sr i = 0.7090），该转变与 Merensky 装置记录的东肢和西肢的同位素转变相匹配。因此，这一新的 Sr 同位素数据表明，Flatreef 的主要矿化层段可以在地层学上与 BIC 其余部分的 Merensky Reef 相关。此外，我们将这些结果解释为令人信服的证据，表明 Flatreef 的主要矿化过程可能与东部和西部边缘的矿化过程相似，并且与当地乡村岩石的相互作用不是必要条件。