Ovalle J Tomás, La Cruz Nikita L, Reich Martin, Barra Fernando, Simon Adam C, Konecke Brian A, Rodriguez-Mustafa María A, Deditius Artur P, Childress Tristan M, Morata Diego
Department of Geology and Andean Geothermal Center of Excellence (CEGA), FCFM, Universidad de Chile, Plaza Ercilla 803, Santiago, Chile.
Department of Earth and Environmental Sciences, University of Michigan, 1100 North University Avenue, Ann Arbor, MI, 48109-1005, USA.
Sci Rep. 2018 Oct 5;8(1):14855. doi: 10.1038/s41598-018-33206-3.
The genetic link between magmas and ore deposit formation is well documented by studies of fossil hydrothermal systems associated with magmatic intrusions at depth. However, the role of explosive volcanic processes as active agents of mineralization remains unexplored owing to the fact that metals and volatiles are released into the atmosphere during the eruption of arc volcanoes. Here, we draw on observations of the uniquely preserved El Laco iron deposit in the Central Andes to shed new light on the metallogenic role of explosive volcanism that operates on a global scale. The massive magnetite (FeO) ore bodies at El Laco have surface structures remarkably similar to basaltic lava flows, stimulating controversy about their origin. A long-standing debate has endured because all proposed models were constructed based exclusively on samples collected from surface outcrops representing the uppermost and most altered portion of the deposit. We overcome this sampling bias by studying samples retrieved from several drill cores and surface outcrops. Our results reveal complex lithological, textural and geochemical variations characterized by magmatic-like features and, most notably, a systematic increase in titanium concentration of magnetite with depth that account for an evolving system transitioning from purely magmatic to magmatic-hydrothermal conditions. We conclude that El Laco, and similar deposits worldwide, formed by a synergistic combination of common magmatic processes enhanced during the evolution of caldera-related explosive volcanic systems.
通过对与深部岩浆侵入相关的古热液系统的研究，岩浆与矿床形成之间的遗传联系已有充分记录。然而，由于弧火山喷发期间金属和挥发物会释放到大气中，爆发性火山作用作为成矿的活跃因素的作用仍未得到探索。在此，我们利用对安第斯中部保存极为完好的埃尔拉科铁矿床的观察，来揭示在全球范围内起作用的爆发性火山作用的成矿作用。埃尔拉科的块状磁铁矿（FeO）矿体的表面结构与玄武岩熔岩流极为相似，引发了关于其成因的争议。一场长期的争论一直持续着，因为所有提出的模型都完全基于从代表矿床最上部和变化最大部分的地表露头采集的样本构建。我们通过研究从多个钻孔岩芯和地表露头获取的样本克服了这种采样偏差。我们的结果揭示了复杂的岩性、结构和地球化学变化，其特征为具有类似岩浆的特征，最显著的是磁铁矿的钛浓度随深度系统性增加，这表明该系统从纯岩浆条件向岩浆 - 热液条件转变。我们得出结论，埃尔拉科以及全球类似的矿床是由与破火山口相关的爆发性火山系统演化过程中增强的常见岩浆过程协同组合形成的。
