Breccias of Svoboda ore area of Malmyzhskoe gold-copper porphyry deposit (Khabarovsk territory)

Abstract

The texture and variety of types of breccia bodies of the ore section of the Svoboda at the Malmyzhskoye deposit have been studied and described: a large one — the complex structure of eruptive (hydrothermal-magmatic) breccias and a relatively small — the columnar body of phreatic breccias. Eruptive breccias are intra-ore with respect to gold-copper mineralization. The detrital part in them is represented mainly by metasomatically altered intrusive rocks of the 1st phase of introduction and sedimentary formations of the cretaceous Largasinsky suite. Breccia cementing material is potassium feldspar-quartz-chlorite-sericite mass, which is an intensively metasomatically altered rock of the 2nd intrusive phase of intrusion. Ore mineralization in breccias has a veindisseminated texture and is part of the clastic part of breccias and is also superimposed on the already formed breccia bodies in the process of their metasomatic alternation. Phreatic breccias formed at the final stages of the development of the porphyry system. They are distinguished by low copper and gold contents and sharp secant contacts with the rocks surrounding them. The composition of the debris is generally similar to eruptive breccia, cement is quartz-sericite-epidote-chlorite. The position of ore mineralization is similar to that in eruptive breccias, but it is manifested to a much lesser extent. According to the proposed genetic model, the formation of the body of eruptive breccias occurred as a result of fluidization of rocks located in the arches of the intrusive body, followed by the introduction of significant volumes of magmatic melt. Subsequently, when rising, the fluids interacted with the cold near-surface waters, which caused the formation of phreatic breccias. The studied features of breccia formations are in a good agreement with the classical model of copper-porphyry deposits of the world.