Shape and Size Distribution of Sulfide Globules in the Raglan Magmatic Sulfide Deposit: Implications for Deposition and Exploration of Massive Sulfide Orebodies
Authors: Li Ying Zhou , Mungall James E. 
Published: November 2024

Abstract
Globular sulfide is the best-preserved textural representation of immiscible sulfide liquids in silicate magmas, containing valuable information about the mechanisms of their transport and deposition and the formation of magmatic sulfide deposits. Previous studies have indicated that sulfide globule textures may convey useful information about their proximity to massive sulfide accumulations. This study quantitatively evaluates the genetic and spatial relationships between globular sulfides and massive orebodies in Zones 8 and 14 of the Raglan Horizon of northern Quebec by investigating their geochemical characteristics and systematically measuring globule size distributions (GSDs) across this portion of the Raglan deposit group. Their compositions suggest that sulfide globules, disseminated sulfides, net-textured sulfides, and massive sulfides in Zones 8 and 14 are genetically related and geochemically indistinguishable. The sulfide GSDs show that most samples taken from locations distal to massive lenses exhibit a simple log-linear relationship resembling the result of a single homogeneous nucleation event with linear growth and relatively constant nucleation density, or disaggregation of sulfide droplets by ligament stretching. In contrast, most samples of the proximal population show kinked GSD shapes. The kinked profiles can be attributed to processes possibly including mechanical sorting, Ostwald ripening, coalescence of sulfide globules, or the mixing of two globule populations with different size distributions. Whereas mechanical sorting, Ostwald ripening, and coalescence between sulfide globules are considered as, at most, minor contributors to the GSD shapes observed in this region, the kinked GSDs are best explained as representations of a mixed population of large, transported globules deposited in an early stage and finer-grained sulfide droplets deposited in a latter stage. Based on these interpretations, an ore-forming mechanism is proposed which starts with (1) deposition of large sulfide globules in a footwall embayment during turbulent magma flow in which the finer globules remain in suspension, followed by (2) the deposition and entrapment of fine-grained sulfide microdroplets due to a transition from turbulent to a transitional or laminar flow regime, and eventually (3) the rapid downward percolation of sulfide microdroplets through the pore network of the cumulate pile to form massive sulfide pools on the hard substrate of the footwall embayment. Furthermore, we find a close spatial relationship between samples with kinked GSDs and high globule number densities and massive sulfide ores. We demonstrate the robustness of using globule number density as a pointer to massive sulfide accumulations by successfully predicting the actual locations of orebodies 8M, 14K, and 14J in a 3-D space. Overall, we suggest that the texture of large globules immersed in finely dispersed clouds of abundant disseminated small sulfide globules is a strong indicator for proximity to massive sulfide accumulations, and the recognition of this texture may provide a critical tool for future exploration for massive magmatic sulfide ore lenses. We present schematic illustrations of favorable and unfavorable GSDs to aid in the qualitative application of these concepts during logging of exploration drill core.