The role of evaporite layers in the ore-forming processes of iron oxide-apatite and skarn Fe deposits: Examples from the middle-lower Yangtze River metallogenic Belt, East China

Involvement of Evaporite Layers in the Formation of Iron Oxide-Apatite Ore Deposits: Examples from the Luohe Deposit in China and the El Laco Deposit in Chile

“…(1) The pyrite δ 34 S V-CDT values are markedly positive, higher than that of mantle-derived magma and lower than that of anhydrite in the ore body. (2) All anhydrite in the ore body is significantly enriched in 34 S relative to pyrite, and the δ 34 S V-CDT values are similar to those of anhydrite from the evaporite layers (n = 3, average of 29.7‰) in the Dongma'anshan Formation near the ore district [18]. Therefore, sulfur in the Luohe IOA deposit is probably sourced from a mixture of primitive magma and evaporite layers.…”

“…Sulfur isotopes can provide important constraints on the origin of sulfur in ore deposits [47,50,72]. Sulfide (pyrite) and sulfates (gypsum/anhydrite), with unique diopside-gypsum-magnetite (gypsum-pyroxene) and garnet-gypsum-magnetite assemblages, are developed in the Luohe and El Laco IOA deposits [2,4,18,38,64,73]. The relative 34 S enrichment in sulfates is much larger than that in sulfides [72].…”

“…The sulfur isotope compositions of pyrite and gypsum at Luohe are shown in Table 2 [18,38,61,73,75]. The results yield a range of δ 34 S V-CDT values from −14.0‰ to 11.1‰ (n = 174, average of 4.2) for pyrite and 13.6‰ to 24.4‰ (n = 126, average of 18.1) for anhydrite.…”

“…Iron oxide-apatite (IOA) deposits, also known as magnetite-apatite deposits or Kirunatype deposits, are an important type of porphyrite Fe deposits that occurred sporadically over a considerable time span ranging from the Paleoproterozoic to the Pliocene; they are mainly found at convergent boundaries, such as the Kiruna and Grängesberg districts in Sweden, the Bafq and Zanjan districts in Iran, the Great Bear zone in Canada, the Adirondack and Missouri districts in the United States, the High Andes and iron belt in Chile, and the Ningwu and Luzong districts in eastern China . IOA deposits are characterized by massive and disseminated magnetite-apatite ± actinolite ores with Na, Ca, and K alteration and have a close spatial relationship with evaporite layers [2,4,18,[23][24][25][26][27][28][29], which dominantly comprise gypsum/anhydrite, halite, and carbonates [2,[30][31][32][33]. However, whether the evaporite layers are involved and play an important role in the formation of IOA ore deposits remains controversial.…”

“…However, whether the evaporite layers are involved and play an important role in the formation of IOA ore deposits remains controversial. As the most important oxidation barrier, assimilation of evaporate layers played a key role in the formation of IOA deposits [2,4,14,18,23,26,28,29], while other researchers argue that evaporate layers are not needed to form IOA deposits [13].…”