Genesis of magnesite–talc–brucite deposits in Paleoproterozoic Mg-rich carbonate formations, Liaodong Peninsula, northeast China

• Metamorphism causes Mg loss as dolomite, enriching magnesite orebodies. • Silica-rich hydrothermal fluids metasomatize magnesite to talc, inducing Mg isotope kinetic fractionation. • Complete magnesite-to-brucite transformation avoids significant Mg isotope kinetic fractionation. • Mg-rich carbonate formations (parent & host rock) endow Mg-bearing nonmetallic deposits with genetic affinity. Large amounts of magnesite, talc and brucite deposits are hosted within Paleoproterozoic magnesium carbonate formations on the Liaodong Peninsula, northeast China. To clarify the genetic relationships of these Mg-rich nonmetallic ore deposits, this study reviewed existing geological, geochemical and isotopic data of magnesite and talc deposits, and supplemented geochemical and magnesium isotope analyses on brucite deposit. The Veitsch-type magnesite deposits on the Liaodong Peninsula occur as stratabound monoclinal orebodies within the Dashiqiao Formation and exhibit inherited marine stable isotopic characteristics ( δ 26 Mg: between −1.53‰ and −0.49‰; δ 13 C: between −2.7‰ and + 1.6‰). The talc ore bodies are clearly controlled by regional folds and fault structures formed during the Lvliangian movement(1.9 Ga ∼1.8 Ga). Interlayer faults are the most favorable sites for the formation of talc ore bodies, which result from reactions between metamorphic-related siliceous hydrothermal fluids and dolomitic magnesite, whose magnesium isotopic composition ( δ 26 Mg: between −0.48‰ and + 1.06‰) no longer reflects marine geochemical characteristics. Brucite ore bodies occur as lenticular forms within carbonate strata in skarn-type external contact zones of granitic rocks that formed during the Phanerozoic era. These ore bodies are formed through the heating of atmospheric precipitation by magmatic bodies that subsequently reacts with carbonate rocks, and they still retain a marine-like REE distribution pattern and magnesium isotope characteristics (range from −1.33‰ to −1.13‰). Therefore, the nonmetallic magnesite, talc, and brucite deposits belong to a typical metallogenic series of Paleoproterozoic magnesium carbonate formations, which formed via metamorphic recrystallization, siliceous hydrothermal metasomatism, and late magmatic–hydrothermal mineralization, respectively.