Impurity Elements in the Iron Ore Horizons of the Bakchar Deposit

A. N. Kondakov

(Presented by Professor A. M. Kuzmin)

The paper examines the distribution features of the following elements: V, Mn, As, Ti, Cr, Ni, Co, Cu, Pb, Zn. Of the list given, only for V, Mn, and Ti does the degree of study not fall short of the degree of study of the distribution of iron. For the other elements in the list, the available information is limited and preliminary in character. Four horizons have been distinguished at the deposit: Narym, Kolpashevo, Chigara, and Tym–Bakchar (Bakchar). The ores of the Kolpashevo and Tym–Bakchar horizons are promising for industrial development. The deposits in the horizons are represented by oolitic ores with siderite–chlorite and siderite cements, loose oolitic ores, chloritolites, and oolitic sandstones with chlorite cement. The ores are characterized predominantly by the trivalent state of iron.

Vanadium. Vanadium occurs in the deposits in dispersed form. The highest vanadium contents are characteristic of oolites, and the lowest of siderite (Table 1). There is a close direct correlation between the bulk iron content in the deposits and the vanadium content. The correlation coefficients are +0.91 for the Narym horizon, +0.91 for the Kolpashevo horizon, +0.89 for the Chigara horizon, and +0.92 for the Tym–Bakchar horizon. The coefficients were obtained from data on weighted-average vanadium and iron contents in individual sections of the horizons. A similar value is shown by the correlation coefficient of vanadium and total metallic iron in sandy-clayey low-iron rocks (Table 2). The close correlation between the total iron content and the vanadium content in the deposits is evidently due to the fact that the main mass of vanadium entered the basin in the form of the acid anion \((\mathrm{VO}_4)^{-3}\), sorbed by iron hydroxides. As a result of diagenetic processes, the closeness of the relationship between vanadium and trivalent iron was disturbed toward a decrease both in the ores and in low-iron rocks (Table 2). Vanadium, which is relatively immobile in a reducing environment, was sorbed by the newly formed mineral mass, including clayey leptochlorites. In the deposits of the horizons, vanadium is distributed by repeating the pattern of iso-contents of the total amount of iron.

Manganese. The element has not been found in independent mineral segregations. The highest manganese content has been established in siderite cement, and less in hydrogoethite oolites (Table 1). In the deposits there is a correlation relationship of manganese with oxide and

Table 1

Average contents of elements in ore and rock components
of the iron-ore horizons of the Bakchar deposit

Note: 1—siderite cement, 2—ooids and oolites of goethite–hydrogoethite composition, 3—ooids and oolites of hydrogoethite–chlorite composition, 4—leptochlorite cement, 5—clayey cement, 6—siderite, 7—ore oolites and boboviny, 8—clayey leptochlorites, 9—leptochlorite–clayey fraction.

ferrous iron (Table 2). In loose ores manganese correlates closely with ferric iron; in ores with siderite cement—with ferric and ferrous iron; in ores with siderite–leptochlorite cement—mainly with ferrous iron. Because of the negative relationship between ferric and ferrous iron, the correlation of manganese with the value of the ratio of ferric iron to ferrous iron has a nonlinear hyperbolic character. According to published analyses [6], in leptochlorites the manganese content correlates with trivalent iron and is apparently connected to a significant degree with a finely dispersed admixture of hydrogoethite. The average manganese content in the ores is 0.16–0.26% (Table 3). In the Kerch ores manganese is present in an amount of 0.57–2% [4], in the Khoper ores 0.17–2.88% [7], and in the Ayat ores 0.11–3.1% [2], i.e., in known deposits of similar genesis the manganese content in the ores is higher. The limits of weighted average contents in individual sections of the horizons are 0.08–0.20% for the Narym, 0.08–0.25% for the Kolpashevo, 0.06–0.16% for the Chigarin, and 0.13–0.32% for the Tym–Bakchar horizons. The deposits of the Tym–Bakchar horizon are the richest in manganese (Table 3).

Arsenic. The element occurs in a dispersed state. In hydrogoethite oolites the arsenic content is significantly higher than its content in other minerals (Table 1). In the ores, arsenic is directly and rather closely correlated with the content of ferric iron, especially in loose oolitic ores. In ores with siderite–chlorite cement the closeness of the relationship is expressed much more weakly (Table 2). The probable form of arsenic accumulation is sorption by the positively charged colloid Fe(OH)₃, and in ores with chlorite-bearing cement, by other mineral colloids as well. The average arsenic content in the ores is 0.026–0.036% (Table 3), which is significantly lower than its content in the Kerch ores (0.09–0.13%) [4]. The limits of weighted average contents in sections are 0.01–0.03% for the Narym, 0.01–0.25% for the Kolpashevo, 0.02–0.03% for the Chigarin, and 0.01–0.03% for the Tym–Bakchar horizons.

Titanium. “Visible” mineral segregations of titanium are represented

Table 2

Results of correlation analysis of some components

Note: $x$, $y$—arithmetic mean content, %; $S_x$, $S_y$—mean-square deviation, %; $r$—correlation coefficient; $n$—number of paired determinations.

an insignificant impurity of rutile, anatase, and ilmenite. The titanium impurity has been established in all authigenic and clayey minerals; moreover, chlorites and clayey minerals have the highest titanium content (Table 1). In the hydrogoethite oolites of the Tym-Bakchar horizon, a relatively elevated titanium content has also been established. In ores with siderite-chlorite cement there is a close positive relationship between titanium and aluminum (Table 2). In ores with siderite cement the relationship is absent, and in loose ores the relationship is weak and unreliable. In the ores, attention is drawn to the equal magnitude of the correlation coefficient and its negative character for the pairs TiO$_2$--Fe$_2$O$_3$ and Al$_2$O$_3$--Fe$_2$O$_3$, which confirms the correlation relationship between titanium and aluminum and the absence of a positive relationship with Fe$_2$O$_3$. As is known, the relationship between titanium and aluminum is due to the residual accumulation of finely dispersed TiO$_2$ in clayey weathering products [5], with which titanium oxide is transported as part of fine suspensions. During diagenesis, local migration in the form of a colloidal solution of the oxide and slight sorption enrichment of the iron-hydroxide substance of the oolites are possible. In the ores, the TiO$_2$ content is 0.30--0.45% (Table 3). The average titanium content in the horizons is indicated in Table 3.

Table 3

Average contents of elements and oxides in deposits of ore horizons and in ores of the Bakchar deposit (based on chemical analyses)

Note: Deposits of ore-bearing horizons: 1 -- Tym-Bakchar, 2 -- Chigara, 3 -- Kolpashevo, 4 -- Narym; ores: 5 -- oolitic ores with siderite cement, 6 -- loose oolitic hydrogoethite ores, 7 -- oolitic ores with siderite-chlorite cement, 8 -- weight clarkes of elements in the lithosphere.

In sections of the ore-bearing horizons, the limits of weighted-average contents are 0.29--0.49% in the Narym horizon, 0.29--0.55% in the Kolpashevo horizon, 0.45--0.70% in the Chigara horizon, and 0.29--0.48% in the Tym-Bakchar horizon.

Chromium. The element accumulated predominantly in oolitic material; the chromium content is somewhat lower in clayey-chloritic minerals and minimal in siderite cement (Table 1). According to individual analyses, glauconites have a high chromium content. Glauconite-bearing deposits are characterized by an increased chromium content. Chromium was sorbed by iron hydroxides and, to a lesser extent, by other colloids, both during the sedimentation stage and during the stage of regressive diagenesis, isomorphously replacing Fe$^{3+}$ during recrystallization of colloids. Average contents in sections of the horizons lie within the ranges 0.02--0.05% for the Narym, n/d--0.13% for the Kolpashevo, 0.02--0.07% for the Chigara, and 0.029--0.061% for the Tym-Bakchar horizons. The ores have an average content of 0.039--0.057%, with the lowest content found in oolitic ores with siderite cement. Co-

the chromium content in the ores is significantly lower than its content in the Kerch ores (0.17% [1]).

Nickel. The nickel content in hydrogoethite oolites and in the chlorite-clayey fraction is close to and higher than the nickel content in siderite cement (Table 1). The features of nickel distribution are caused by its constant valence and the high pH value of hydration, equal to 6.7, owing to which the bulk of it accumulated in the lepto-chlorite stage, replacing magnesium during recrystallization of colloids. In the deposits, from the lower to the upper horizon, the average nickel content regularly decreases (Table 3). However, even in the upper Tym–Bakchar horizon, in deposits with clayey cement the nickel content is comparatively high (up to 0.09% against a background of 0.02%). The average nickel content in the ores is 0.018–0.035% and exceeds its content in the Kerch ores (0.008% [1]).

Cobalt. Chemical analyses did not detect cobalt; however, its presence was established by spectral analyses, including quantitative ones. Siderite cement has the minimum cobalt content (Table 1). The distribution of cobalt, analogous to that of nickel, is determined by the close pH value for precipitation of the hydroxides Co²⁺ and Ni²⁺. The weak concentration of cobalt and nickel in the oolites of the Tym–Bakchar horizon is possibly connected with a finely dispersed admixture of asbolane in them.

Copper. Copper is distributed fairly uniformly in the mineral components, slightly enriching the hydrogoethite oolites (Table 1). The main reason for the accumulation of copper in sediments of this kind is sorption; according to the studies of M. F. Kashirtseva [3], favorable sorbents are the hydroxides of iron, aluminum, and silicon, and, to a lesser degree, clays. The copper content in the deposits of the ore-bearing horizons is in the range 0.02–0.027%, and in the ores 0.013–0.021% (Table 3).

Lead. The results of semiquantitative analysis show that, on average, oolitic material and siderite cement have a higher lead content than the leptochlorite-clayey fraction (Table 1). Sorption processes played the leading role in the accumulation of lead. According to E. V. Rozhkova and O. V. Shcherbak [8], favorable sorbents are the hydroxides of iron and aluminum and, secondarily, clay minerals. Part of the lead was apparently preserved in silt solutions and precipitated in carbonate form together with siderites. The lead content in the ores is 0.012–0.014% and in the deposits of the ore-bearing horizons 0.008–0.013% (Table 3).

Zinc. Zinc accumulated predominantly in siderite, less in the oolitic material, and the lowest zinc content was noted in the clayey fraction (Table 1, semiquantitative analyses). In siderites there is a close direct correlation between zinc and magnesium (Table 2), indicating isomorphic replacement of the latter by zinc. In other minerals, sorbed and isomorphic forms of occurrence are possible. In contrast to the sparingly soluble compounds of lead, the solubility of zinc salts is significantly higher, and it could have remained in large quantities in solutions by the time carbonate minerals precipitated. According to the scant available data, ores with siderite cement have a higher zinc content than loose oolitic ores (Table 3).

Of the elements listed, V, Mn, and Ti are of substantial importance in the ores. The first is characterized by a relationship with the total iron content. The relationship is so close that, for prospective calculations, one can use the equations of the correlation relationship without resorting to chemical-

... chemical analyses. Hydrogoethite ores and especially ores with siderite cement are more promising with respect to elevated manganese content than ores with chlorite cement; at the same time, the latter are characterized by an elevated titanium content and its close association with aluminum.

REFERENCES

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