Source Characteristics of the Carboniferous Ortokarnash Manganese Deposit in the Western Kunlun Mountains

Abstract

The specific source of ancient sedimentary manganese (Mn) deposits is commonly complex. Here we use systematic major and trace element data with strontium (Sr) and neodymium (Nd) isotopic analyses of the Ortokarnash Mn(II) carbonate ores and associated carbonate rocks from the Upper Carboniferous Kalaatehe Formation (ca. 320 Ma) in order to constrain the Mn source. This formation consists of three members: the first member is a volcanic breccia limestone, the second member is a sandy limestone, and the third member is a black marlstone with the Mn(II) carbonate interlayers. Petrographic observations in combination with low Al2O3 (<3.0 wt%) and Hf (<0.40 ppm) contents and the lack of correlations between the Al2O3 and 87Sr/86Sr ratios as well as εNd(t) values demonstrate a negligible influence of terrigenous detrital contamination on both Sr and Nd isotopic compositions of the Mn(II) carbonate ores. The Sr isotopes of Mn(II) carbonate ores are most likely affected by post-depositional alteration, while Nd isotopes remain unaltered. The initial 87Sr/86Sr ratios in the associated carbonate rocks are likely the result of a mixture of the chemical components (i.e., seawater) and the Al-rich components (e.g., volcanoclastic material), while the detrital effects on Nd isotopes are negligible. In addition, both Sr and Nd isotopes in these non-mineralized wall rocks remained unchanged during post-depositional processes. The relatively low Th/Sc ratios and positive εNd(t) values suggest that the aluminosilicate fraction in the calcarenite and sandy limestone was mainly derived from the weathering of a depleted mafic source, representing the riverine input into the seawater. Given that the Mn(II) carbonate ores are characterized by negative εNd(t) values, these suggest that seafloor-vented hydrothermal fluids derived from interaction with the underlying old continental crust mainly contribute to the source of the Mn(II) carbonates.

Magmatic–Hydrothermal Origin of Fe-Mn Deposits in the Lesser Khingan Range (Russian Far East): Petrographic, Mineralogical and Geochemical Evidence

“…For example, LKR ores plot into the field of hydrothermal Fe-Mn formations in (Ce/Ce*) N − (Y/Ho) N , Si-Al, Fe-Mn-(Co + Ni + Cu) × 10 and (Co + Ni) − (Zn + Cu + V + Pb) discrimination diagrams for Fe-Mn mineralization [68]. Various geochemical indicator ratios in most iron-manganese ores from the LKR such as (Mn + Fe)/Ti , Ba/Ti (>0.15), Y/Ho (21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32)(33)(34)(35), (Y/Y*) N (>1), (Eu/Eu*) N (>1), along with relatively low total REE + Y (<100 ppm) and Th (0.46-7.93 ppm), are compatible with the hydrothermal origin of iron and manganese minerals in the LKR. In particular, the positive Eu anomaly and the lack of a negative Ce anomaly in the majority of ore samples from the LKR deposits argue against any substantial role of seawater precipitation in the formation of Fe-Mn oxides and hydroxides [112][113][114][115][116].…”

“…Iron and iron-manganese deposits in orogenic belts of different ages contain substantial resources of these important industrial metals and include different genetic types such as iron oxide-copper-gold (IOCG), Kiruna-type iron oxide-apatite (IOA; apatite-magnetite), sedimentary exhalative, magmatic-hydrothermal, volcanogenic (Cuban-type) and skarntype deposits, as well as many other subtypes of Fe-Mn mineralization . These "orogenic" deposits experienced variable scale contributions from a wide range of magmatic, hydrothermal, sedimentary and biological sources and processes [9,14,15,17,25,29,[31][32][33][34][35][36][37][38][39][40][41][42][43]. A separate group of skarn-style magnetite mineralization (Cornwall-type deposits) has been documented in Pennsylvania and North China cratons in relation to interactions between basaltic magma, ore-forming fluids and host shale, sandstone and carbonate [44][45][46].…”