A multi-isotope approach towards constraining the origin of large-scale Paleoproterozoic B-(Fe) mineralization in NE China

Abstract

Borate ore deposits occur predominantly in Phanerozoic evaporative sedimentary environments but are scarce in Precambrian strata. However, massive B-and Mg-rich borate deposits are abundant in the Paleoproterozoic strata of Northeast (NE) China. In addition, several of these borate deposits are dominated by Fe (e.g., >60% Fe2O3 content in the Wengquangou deposit). To constrain the origin of these unusual deposits, we obtained B, Fe, and Mg isotope data on the wall rocks and ores of the Mg-rich Houxianyu borate deposit and the Fe-rich Wengquangou borate deposit in NE China. The δ 11 B values of the borate deposits (10.66 ± 4.35‰, n = 15) are higher than most types of igneous andThe final publication is available at Elsevier via

Petrological and Geochemical Constraints on the Protoliths of Serpentine‐Magnetite Ores in the Zhaoanzhuang Iron Deposit, Southern North China Craton

“…The other low-Ti picritic or basaltic magma could also evolve into low-Ti iron oxide deposit via crystallized differentiation or liquid immiscibility, such as the low-Ti iron oxide deposits in the Emeishan large igneous province (ELIP) related to low-Ti basalts and grabbroic intrusions . High-Mg sediments on the earth are often associated with seawater carbonate precipitation, such as Mg-rich borate deposits in the Lieryu Formation of China, which may have formed directly through precipitation of Mg-rich seawater or diagenesis via Mg-rich brine in an evaporative sedimentary environment (Chen Congxi et al, 2003;Hu Guyue et al, 2014Dong et al, 2016Dong et al, , 2017 and magnesite deposit in other countries (Pohl, 1990;Melezhik et al, 2001;Frank and Fielding, 2003;Henjes-Kunst et al, 2014 (Arora et al, 1995;Xu et al, 2014). And furthermore, the low-Ti iron ore deposit derived from this low-Ti basaltic magma was considered to be associated with liquid immiscibility of low-Ti Fe-rich melts, generally forming apatite-magnetite ores , rather than Mg-rich magnetite ores from Zhaoanzhuang iron deposit.…”

“…Similar Mg-rich and Ti-poor iron deposits also occur in other areas of the North China Craton, including the Lilaozhuang magnesite-magnetite deposit hosted in the Neoarchean-Paleoproterozoic Huoqiu Group (Huang Hua et al, 2013), and the Lieryu boron-magnesite-magnetite deposit (Feng Benzhi et al, 1995;Sun Houjiang and Wu Chunlin, 1996;Dong Aiguo, 2016) hosted in the Paleoproterozoic Liaohe Group (Fig. And Lieryu boron-magnesite-magnetite deposit located in the northern margin of the NCC, has been considered to be derived from Mg-rich marine carbonate rock that had experienced evaporative process (Hu Guyue et al, 2014Dong et al, 2016Dong et al, , 2017. The origin of the Lilaozhuang magnesite-magnetite deposit is debated, with recent studies assigning a similarity with BIF (generally pronounced positive Eu anomalies and depletion of light REE and enrichment of heavy REE), which was formed in a confined oceanic basin along continental margin (Huang et al, 2017).…”

“…Therefore, the high-Mg/low-Ti nature of the Zhaoanazhuang iron ore is inconsistent with maficultramafic intrusion-associated iron ores, Fe-Mg-Si-rich sedimentary sequence as a protolith can well fit the features above. High-Mg sediments on the earth are often associated with seawater carbonate precipitation, such as Mg-rich borate deposits in the Lieryu Formation of China, which may have formed directly through precipitation of Mg-rich seawater or diagenesis via Mg-rich brine in an evaporative sedimentary environment (Chen Congxi et al, 2003;Hu Guyue et al, 2014Dong et al, 2016Dong et al, , 2017 and magnesite deposit in other countries (Pohl, 1990;Melezhik et al, 2001;Frank and Fielding, 2003;Henjes-Kunst et al, 2014). The primitive mantlenormalized trace element spider diagrams (Figs.…”

“…The origin of the Lilaozhuang magnesite-magnetite deposit is debated, with recent studies assigning a similarity with BIF (generally pronounced positive Eu anomalies and depletion of light REE and enrichment of heavy REE), which was formed in a confined oceanic basin along continental margin (Huang et al, 2017). And Lieryu boron-magnesite-magnetite deposit located in the northern margin of the NCC, has been considered to be derived from Mg-rich marine carbonate rock that had experienced evaporative process (Hu Guyue et al, 2014Dong et al, 2016Dong et al, , 2017. Tectonically, the Zhaoanzhuang iron deposit and Lilaozhuang magnesite-magnetite deposit belong to the same metallogenic belt located in the southern part of the NCC and the ore-bearing strata are also comparable , possibly revealing their similar protolith.…”

Stable Isotope (S, Mg, B) Constraints on the Origin of the Early Precambrian Zhaoanzhuang Serpentine-Magnetite Deposit, Southern North China Craton

“…Mg isotopic fractionation is very sensitive to low-temperature processes, such as Mg-calcite, dolomite, and magnesite precipitation, continental and chemical silicate weathering, and biological processes [48][49][50][51][52][53][54][55][56][57][58]. However, it is limited during partial melting, crystal fractionation, and low-to high-temperature metamorphic processes [47,[59][60][61][62][63][64][65][66]. Igneous rocks, ranging from peridotite to granite, and magmatic minerals (olivine, orthopyroxene, clinopyroxene, and hornblende) generally have identical chondritic Mg isotopic compositions (average δ 26 Mg = −0.25 ± 0.07% ) [47,[59][60][61][62][67][68][69].…”