Geochemical exploration and baseline from marine sediments in the fjords, channels and straits of Magellan, Chilean Patagonia

Abstract

Chilean Patagonia has a complex geological history dominated recently by Quaternary glaciers and rivers that have carried sediments from the mountains to depositional environments within marine fjords and channels. Although much is known about onshore placer deposits, little is known about these deposits and depositional systems in the offshore realm. This study analyzes the chemistry and mineralogy of marine sediments collected in the Strait of Magellan and around the region. This study aims to comprehend the distribution, concentration and provenance of critical/strategic elements and precious metals. In collaboration with the Cabo de Hornos research vessel of the Chilean Navy, 63 sediment samples were collected using a box core sampler, complemented with coastal beach samples. These samples underwent petrographic and geochemical analysis. The predominant opaque minerals identified in these samples are mainly iron oxides (magnetite–hematite‐ilmenite) and sulfides (pyrite, exceptional greigite). A comparison of the average element concentration for all samples for different baseline values revealed the following findings. As, Bi, Li, Re, Sb, Se, Te, and Pd exhibit positive anomalies for the Upper Continental Crust (UCC); Re, Se, and Sr. exhibit positive anomalies for Marine Sediments (MS), and Bi, Cs, Li, Re, Se, Sn, and Te show positive anomalies relative to the Folded Belt (FB). The main contrast anomalies occur in the following locations. Almirantazgo Sound (Sn, Ba, Sb, and Tm); Concepción Channel (Re, Sr., and Te); Smyth Channel (Mn, Re, Sb, Sr., Te, and Se); Almirante Montt Gulf (Mn, Re, and Sb); Nelson Strait (Re, Sr., and Te); Ancho Pass (Ti and Sr); Europa Fjord (Bi and Sn); Del Hambre Pass (Sr); Magdalena Channel and Sound (Sr); Froward Pass (Se), and Whiteside Channel (Mn). Regarding precious metals, silver exhibits contrasting anomalies relative to the UCC in seafloor sediments in the Almirante Montt Gulf (0.161 ppm) and Concepción Channel (0.101 ppm). Palladium contrast anomaly is observed in the Peel Estuary (8 ppb) and Platinum contrast anomalies occur in the Concepción (3 and 5 ppb) and Smyth Channels (4 ppb). Finally, gold, in comparison to the South Patagonian Batholith, reveals contrasting anomalies that occur in the Concepción Channel (8 ppb), Peel Estuary (6.7 and 8 ppb), Nelson Strait (7 ppb), Almirante Montt Gulf (6 ppb), Forward Pass (8 ppb), and Ancho Pass (7 ppb). In summary, the presented results provide valuable insights into the geological and geochemical baseline of the region, offering a better understanding of the relationship with depositional basins and source zones onshore during the late‐Quaternary.