Siderite chemical composition

EPMA data (Table 1) typically show small amounts of Ca and Mg, and traces of Mn in siderite. Chemical composition is relatively constant from one spherule to another within the same thin section. Individual rhombs and spherules show a systematic peripheral enrichment in Ca arid Mg relative to the core (Table 1). 

The Renison Bell tin mine is a large, but complex, oxide mineral deposit. Renison ore consists largely of pyrrhotite, quartz, dolomite, siderite and dorite. The chemical composition of the iron varies considerably. Some of the ore types are high in copper and silver. Table 21.5 shows the chemical analyses of various ore types. 

The chamosites in individual sedimentary iron formations vary widely in color which indicates there is considerable local variation in chemical composition. The sedimentary chamosites are usually quite impure, frequently containing siderite and goethite. It is necessary to make a number of assumptions in recasting analyses of these samples. 

The sample suite from each core can be divided into four factors on the basis of similarities in chemical compositions as defined by Q-mode factor modeling. Factor-1 samples are rich in trace metals due to adsorption onto clay, altered tuffaceous material, and (or) organic matter and precipitation as sulfides. The relatively high concentration of boron is probably related to its inclusion in authigenic feldspars. Factor-2 samples are rich in elements commonly associated with minerals of detrital or volcanic origin. These samples contain relatively high concentrations of analcime, dawsonite, and (or) potassium feldspar, all of which are associated with alteration of tuffaceous material. Siderite and ferroan or ankeritic... 

Table 4. Summary table showing the average isotopic, chemical composition and fluid inclusion characteristics of the main siderite cement generations (SI, S2, S3)...

Siderite studied in this research was fi om Xinjiang and chemical composition of the ore sample are shown in Table I. The result indicates that the major chemical components are Fe, Si02 and CaO, and the ore is low in phosphorus but high in sulfur. 

Table I. Chemical Composition of Studied Siderite Sample /%...

Both rust and oxide scales are usually mixtures of iron oxides vith other Fe (e. g. siderite) and non-Fe compounds (CaCOs). In some cases there is a more or less random mixture of components, vhereas in others, the different oxides are arranged in layers to form duplex or triplex scales. Layer-type rust arises as a result of potential or chemical gradients across the film. As these gradients vary ivith film thickness, the composition of the rust changes with the distance from the metal. On the whole, if Fe " and Fe" are present, the oxide containing Fe" is found in the inner layer of the rust. 

The REE patterns of the two siderites (Nos 15 and 16 in Fig. lOA) are alike. Along with the O, C and Sr isotope data (see above), this confirms that the chemical and isotopic compositions of siderite were controlled by fluid composition at a regional scale. 

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