Manganiferous Iron Ore Deposit and its Thermal Metamorphism at Ta-Li-Tzu Iron Mine, Manchuria

Abstract

Ta-Li-Tzu Iron Mine lies south-west of Lin-Chiang, along the upper stream of the River Ya-Lu-Chiang. This district is composed mainly of Proterozoic sediments or schistose metamorphic rocks, though biotite-granite has intruded into the Proterozoic rocks at the head portion of the, Valley Ta-Li-Tzu.
Ta-Li-Tzu Iron Mine is the most important iron mine in Eastern Manchuria, and the iron ore deposits in this mine can be divided into three types. One of them is a, hematite ore bed or vein?, intercalated with the Lower Proterozoic phyllite formation, probably of the Kai-Ping Series, and forms a most profitable iron ore deposit with a high grade ore. The next one is the Upper Proterozoic mang-aniferous iron ore bed described in detail in this paper. The third one is the skarn-like iron silicate mass in the thermally metamorphosed Upper Proterozoic quartzite, and it has been demonstrated to be a thermal metamorphic derivative of the ore of the second type.
The manganiferous iron ore, which has been called by some to be a chamosite iron ore as well as a pisolitic iron ore, forms a bed of two meters or more in thickness, but sometimes it thins out to a mere trace. This ore has a marked pisolitic structure. The pisolites are 0.5-2.0 cm in diameter, con-sisting mainly of the alternation of iron-chlorite-hematite onior-skin layers with more or less fine, scattered siderite, manganosiderite and fine quartz sand. It is also conspicuous that the nuclei of the pisolites are usually composed of fragments of matrix, in which exist a considerable amount of angular or subangular fine quartz sands. The minerals constituting the matrix are mainly manganosiderite and quartz sand, with variable amounts of iron-chlorite and hematite.
The thermal effect of the biotite-granite, probably of Cretaceous intrusive, given to the ore begins with the diminishing or disappearing of fine siderite scattered originally in the pisolite iron-chlorite, forming magnetite grains by its decomposition. Other component minerals such as manganosiderite and iron-chlorite have merely been recrystallized.and increased in their grain size.
The effect of high grade thermal metamorphism can be observed near the contact of the graniteat the head of the Valley Ta-Li-Tzu. In this case the manganiferous iron ore has changed to skarn-like, massive, dark gray ore, but the question of the origin of this peculiar ore can be resolved by the existence of the relic of pisolitic structure in some examples and also by the resemblance of its chemical composition to the manganiferous iron ore, though some of the chemical components such as carbon dioxide have been totally lost.
In the special example of the skarn-like ore, which retains its original piosolitic structure after its mineralogical reconstitution, the pisolite consists of almanditic garnet, magnetite and hematite. The matrix, on the other hand, is composed of knebelite, dannemorite and a little of tephroite. These mineral composition possibly correspond clearly to the original one, without wider diffusion of elements, though some silica should have been obtained from granitic emanation.