Geochemical characteristics of different iron ore types from the Southern Tomašica deposit, Ljubija, NW Bosnia

Abstract

Pulverized limonite ore from a Pleistocene–Quaternary lake deposit and compact limonite ore from the Olistostrome member of the Javorik flysch formation, in the Southern Tomašica iron ore deposit, were investigated and compared with different types of siderite and ankerite, limestone and carbonate shale from the same location in order to determine their possible protolith. Two limonite types display a notably distinct REE pattern, REE fractionations, Eu anomalies and other trace element and main oxide content. The REE pattern of compact limonite is characterized by relatively low light ((La/Sm) N = 2.87), heavy ((Gd/Yb) N = 0.98) and total ((La/Yb) = 3.19) REE fractionations, a strong positive Eu anomaly (Eu/Eu* = 2.11) and weakly expressed negative Ce anomaly (Ce/Ce* = 0.82). The compact limonite and siderite REE patterns almost overlap suggesting a common REE source. The same is valid for their Zr/TiO2 N  ratios (0.040 in the compact limonite, 0.033–0.053 in the siderites). Pulverized limonite shows remarkably different REE patterns and the highest REE concentrations, (up to 6 to 13 times higher relatively to the other samples). Its REE fractionation pattern ((La/Sm) N  = 3.68, (Gd/Yb) N = 1.58, (La/Yb) N = 9.41, Eu/Eu* = 1.10 and Ce/Ce*= 0.81) is very similar to those in the carbonate shale, identifying it as the possible protolith of pulverized limonite. The same is valid for the Zr/TiO  ratios (0.025 in pulverized limonite and 0.017 in carbonate shale). The REE pattern of fine grained ankerite ((La/Yb) 2 N = 2.15, Eu/Eu* = 1.95, Ce/Ce* = 0.78) and its Zr/TiO  ratio (0.030) are similar to those in siderite, and could, assuming extensive contamination of pulverized limonite, also represent its protolith. However, the REE patterns of coarse grained ankerite exhibit remarkable depletion of LREE over HREE and a strong reverse LREE pattern ((La/Yb) N  =0.05–0.20, (La/Sm) N = 0.04–0.10, (Gd/Yb) N 2 = 1.77–1.91). They have (similar to the other studied samples), a positive Eu anomaly (Eu/Eu* = 2.16–2.75) and negative Ce anomaly (Ce/Ce* = 0.32–0.83). Their Zr/TiO  ratio (0.004–0.010) excludes coarse grained ankerite as the possible protolith of pulverized limonite. 

Keywords

• Compact limonite, pulverized limonite, REE pattern, siderite, ankerite, Southern Tomašica