Genesis Of The 1.45 Ga Kratz Spring Iron Oxide-Apatite Deposit Complex In Southeast Missouri, USA: Constraints From Oxide Mineral Chemistry

Seven major and numerous lesser Fe oxide occurrences within the 1.47 Ga St. Francois Mountains terrane in Missouri (USA) have previously been described as iron oxide-apatite (IOA) and iron oxide-copper-gold (IOCG) deposits. Researchers speculate that these contain significant amounts of critical minerals, most notably rare earth elements and cobalt. One of the less-studied deposits in the region is the 1.455 Ga Kratz Spring deposit. The deposit consists of two steeply dipping magnetite bodies beneath 450 m of sedimentary cover. The genesis of the Kratz Spring deposit and its relationship to nearby IOA-IOCG deposits remains poorly constrained. To better understand the formation of the Kratz Spring deposit, the authors integrated stratigraphic, petrographic, and bulk rock studies within situ trace element and Fe isotope chemistry of magnetite and hematite. These data show that the Kratz Spring deposit is hydrothermal in origin but is divided into two sub deposits according to different fluid sources and formation conditions: (1) a deep but cooler hydrothermal Kratz Spring South deposit with a juvenile fluid source and (2) a shallow but hotter magmatic-hydrothermal Kratz Spring North deposit with variable fluid sources. Our genetic model suggests the two Kratz Spring deposits are local expressions of the same mineralization system, i.e., the Kratz Spring South deposit is a distal, lower-temperature offshoot of the feeder system that formed the Kratz Spring North deposit. Understanding the magmatic-hydrothermal plumbing system that formed Missouri\u27s IOA-IOCG deposits is important to guiding critical mineral exploration efforts in the region

Lithology and alteration assemblages of the Boss iron-copper deposit, Iron and Dent Counties, Southeast Missouri

The Boss iron-copper deposit is the only deposit of the Southeast Missouri Iron Metallogenic Province known to contain appreciable copper sulfide mineralization. Major lithologies of Boss West Dome were characterized by petrologic, petrographic and geochemical methods. Previous lithologic classifications inaccurately characterized numerous rock units. Alteration assemblages at West Dome were also characterized and described; those assemblages had not previously been defined. Comparisons of West Dome to other deposits in the Southeast Missouri Iron Metallogenic Province and in the Gawler Province, South Australia, as well as to criteria set forth for Olympic Dam-type deposits, clearly places Boss West Dome in this family of iron-copper-gold deposits. Rhyolites are the earliest lithology, and they are associated with a proposed collapsed caldera complex. Trachytes represent a shallow intrusive that post-dates the rhyolites. Both lithologies exhibit potassium enrichments and secondary quartz emplacement related to a potassic alteration assemblage. A Rb-Sr isotope date of 1.136 Ga ± 0.170 Ga may represent the potassic alteration event. Granitic dikes post-date rhyolites and trachytes. The dikes lack potassium enrichment, suggesting that they were in equilibrium with, or post-dated, potassium alteration. Propylitic, phyllic and hematitic assemblages altered rhyolites, trachytes and granites. Assay values for propylitized core suggest that sulfur associated with this alteration assemblage resulted in additional chalcopyrite mineralization. The phyllic alteration assemblage is one of the most extensive present at West Dome. The extent is unusual in the province. Hematitic alteration may be related to the previously noted assemblages. The assemblages suggest that the Boss deposit formed at shallow depths --Abstract, page iii

Overall survival in the OlympiA phase III trial of adjuvant olaparib in patients with germline pathogenic variants in BRCA1/2 and high-risk, early breast cancer

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