Noble Metals in Arc Basaltic Magmas Worldwide: A Case Study of Modern and Pre-Historic Lavas of the Tolbachik Volcano, Kamchatka

Abstract

Platinum-group elements (PGE) and gold are a promising tool to assess the processes of mantle melting beneath the subduction zones. However, fractionation processes in magmas inevitably overwrite the initial metal budgets of magmas, making constraints on the melting processes inconclusive. Moreover, little is still known about the geochemical behavior of a particular metal in a single arc magmatic system, from mantle melting towards magma solidification. Here we compare noble metals in lavas from several eruptions of the Tolbachik volcano (Kamchatka arc) to better understand the effects of magma differentiation, estimate primary melt compositions and make constraints on the mantle melting. We show that Ir, Ru, Rh and, to a lesser extent, Pt are compatible during magmatic differentiation. The pronounced incompatible behavior of Cu and Pd, observed in Tolbachik magmas, rules out the significant influence of sulfide melts on the early magmatic evolution in this particular case. Gold is also incompatible during magmatic differentiation; however, its systematics can be affected by the inferred gold recycling in the plumbing system of Tolbachik. Although the Tolbachik lavas show only slightly higher PGE fractionation than in MORB, a notable negative Ru anomaly (higher Pt/Ru and Ir/Ru) is observed. We attribute this to be a result of greater oxidation in the subarc mantle (by 1–4 log units), which promotes crystallization of Ru-bearing phases such as Fe3+-rich Cr-spinel and laurite. The estimated Pd contents for the parental melt of the Tolbachik lavas approaches 6.5 ppb. This is several times higher than reported MORB values (1.5 ± 0.5 ppb), suggesting the enrichment of Pd in the mantle wedge. Our results highlight the influence of the subduction-related processes and mantle wedge refertilization on the noble metal budgets of arc magmas.

Nature of Paleozoic Basement of the Catalan Coastal Ranges (Spain) and Tectonic Setting of the Priorat DOQ Wine Terroir: Evidence from Volcanic and Sedimentary Rocks

“…Comparison of Priorat potassic lava (Figure ? ?) with shoshonites, primitive basalts and mantle wedge xenoliths from other subduction environments (Papua New Guinea, Fiji, Kamchatka, Tabar-Lihir-Tanga-Feni arc) [106][107][108][109][110] as well as potassic magmas [107] associated with the world-class supergiant Bingham Canyon Cu-Mo-Au deposit in Utah (USA) indicate some general similarities, but also contrasting differences. The distribution of refractory Ir-group PGEs in Priorat shoshonite is broadly similar to other Late Cenozoic arc-related shoshonites as well as Eocene mineralized shoshonite/absarokite stocks at Bingham Canyon (Figure ??).…”

“…One of the most interesting and exciting-both in the eyes of geochemists and sophisticated wine connoisseurs-wine terroirs must be volcanic tectonic settings [28][29][30][31][32], of which the famous Priorat DOQ region in Catalonia is, in our humble but firm opinion, an almost perfect example. the Mount Hagen volcano, Papua New Guinea [106]; Bingham-potassic lava associated with giant (>500 million tons of ore), high-grade (>1% Cu and >1 g/t Au) Bingham Canyon Cu-Mo-Au deposit, Utah, USA [107]; Fiji-Late Miocene-Early Pliocene shoshonite associated with high-grade (7 g/t Au) Emperor (Vatukoula) epithermal gold deposit (3.6 Moz of contained Au) in Fiji [107]; Lihir-Late Pleistocene (0.36 Ma) shoshonite associated with giant (56 Moz at 2.3 g/t Au) Ladolam low-sulfidation epithermal gold deposit on the Lihir Island in the Tabar-Lihir-Tanga-Feni island arc near Papua New Guinea [107]; Arc basalt-modern primitive (~9 wt.% MgO) calc-alkaline basalt (average of 12 analyses) from the active Tolbachik volcano, Kamchatka arc [108]; Arc mantle-average (16 analyses) composition of depleted mantle wedge-derived peridotite xenoliths from the Avachinsky volcano, Kamchatka volcanic arc [109,110]. Chondrite normalization values are from [44].…”

Formation of Gold Alloys during Crustal Differentiation of Convergent Zone Magmas: Constraints from an AU-Rich Websterite in the Stanovoy Suture Zone (Russian Far East)

“…Gold and other noble metal enrichments were previously reported for both sub-arc mantle sources [19,50,[81][82][83] and subduction-related crustal magmatic conduits [19,36], as well as primitive basaltic and andesitic magmas in volcanic arcs [54,84,85]. The distribution of gold in differentiated arc-related plutonic and volcanic suites suggests that Au behaves as an incompatible element during the fractionation of primitive convergent zone magmas [36,54,85,86].…”

“…Gold and other noble metal enrichments were previously reported for both sub-arc mantle sources [19,50,[81][82][83] and subduction-related crustal magmatic conduits [19,36], as well as primitive basaltic and andesitic magmas in volcanic arcs [54,84,85]. The distribution of gold in differentiated arc-related plutonic and volcanic suites suggests that Au behaves as an incompatible element during the fractionation of primitive convergent zone magmas [36,54,85,86]. This results in the accumulation of precious metals, especially gold, in evolved, late-stage intermediate to felsic residual liquids and contemporaneous enrichment of residual melts in subduction zones in sulfur and magmatic sulfides [20,28,87,88].…”

High Sulfur in Primitive Arc Magmas, Its Origin and Implications

“…This should have led to greater sulfide exhaustion from mantle peridotite and simultaneous enrichment of primary melt by Cu and PGE [3,56]. Indeed, the Tolbachik-1941 lavas are slightly enriched in Cu, Pd, and Pt (up to 234 ppm Cu, 7.8 ppb Pd, and 6.1 ppb Pt) relative to magnesian basalts, e.g., [57]. More importantly, the sulfide globules from Tolbachik [22,28] also contain concentrations of Pd and Pt among the highest ever measured in sulfide globules (up to 299 ppm Pd and 115 ppm Pt, Zelenski et al [58]).…”