Journal of Economic Geology (Dec 2022)
Geochemical and mineralogical evidence on genesis of the Kal-Baneh Mn deposit, north-west of Jiroft, Kerman province
Abstract
The Kal-Baneh Mn deposit is located 56 km northwest of Jiroft city in the southeast of the Sanandaj-Sirjan Zone. The ore mineralization occurs as layered, banded, massive, and disseminated textures within radiolarian cherts of the upper parts of the Esfandaghe ophiolitic complex. The mineralogy is simple and ores consist mainly of pyrolusite and braunite, with trace amounts of hausmannite and hematite. The main gangue minerals are quartz and calcite. Geochemical evidence, including relatively high Mn/Fe (mean=89.39), Si/Al ratios (mean=20), Ba concentrations (mean=842.3 ppm), the low contents of Cu (mean=92.07 ppm), Ni (63.38 ppm), Co (mean=13.04 ppm), Zn (mean=68.15 ppm), total REE (28.1-96.13 ppm), negative Ce (Ce/Ce*: 0.3-0.7), slightly positive Eu (Eu/Eu*: 0.64-1.35) anomalies, the REE pattern of ore samples, and geochemical data reveal a distal hydrothermal-exhalative source and indicate the combination of hydrothermal solutions with seawater. Geochemical signatures, the geometry of orebodies, the nature of the host rock, mineralogy, and the textural features of the manganese ores are consistent with the submarine hydrothermal-hydrogenous Mn deposits. Introduction In the submarine environment, Mn-oxide deposits are classified as hydrogenic, diagenetic, and hydrothermal mineralization corresponding to various processes of formation, rate of precipitation, host rocks, geochemical characteristics, and manganese sources in deposits (Öksüz, 2011; Polgari et al., 2012; Bau et al., 2014). The hydrogenetic iron‐manganese deposits have been slowly precipitated from seawater (2–10 mm/Ma) (Öksüz, 2011) and consist of polymetallic Fe-Mn crusts. These deposits may be identified by rather high concentrations of trace elements in Mn ores (e.g., Co, Ni, Cu, Mo and Zn) (Choi and Hariya, 1992; Hein et al., 1997; Pelleter et al., 2017). Diagenetic Mn deposits are considered to be a result of buried Mn–oxyhydroxide and occur as nodules. In the burial diagenetic processes, Mn–oxyhydroxide is reduced to Mn2+ and bicarbonate is derived from the oxidation of organic carbon (Wu et al., 2016). In such a process, the Mn carbonates (e.g., rhodochrosite; Polgari et al., 2012) are hosted in black shales. Mn-oxide deposits have been precipitated from hydrothermal fluids which generally contain a low concentration of trace elements (Choi and Hariya, 1992; Hein et al., 2008). Although hydrothermal Mn–oxide deposits occur as distal of a massive sulfide ore deposit, they show slightly anomalous contents of trace elements (Hein et al., 2008; Pelleter et al., 2017). The Kal-Baneh Mn deposit is located in the southwest of the Kerman Province, Iran, around 56 km north-west of Jiroft city and 245 km southwest of Kerman in the Sanandaj-Sirjan Zone (Fig. 1). The Sanandaj-Sirjan Zone is one of the main metallogenic provinces in Iran. It hosts several massive sulfides, manganese and ferromanganese deposits. The majority of these deposits are hosted by the Late Triassic to Middle Cretaceous ophiolites. So far, no investigation has been reported on the Kal-Baneh Mn deposit. Nevertheless, petrological studies have been carried out on the southeast margin of the Sanandaj-Sirjan Zone (Sabzehei, 1974; Sabzehei and Youssefi, 2000; Mohajjel and Fergusson, 2000). In this study, we describe the geological and mineralogical data for the Kal-Baneh Mn-oxide deposit in detail and the textural and structural characteristics of the ore minerals. Major, trace, and rare earth element (REE) contents in ore samples were determined. The present study aims to recognize the origin of the deposit and mineralization processes. Materials and methods During the fieldwork, more than 90 hand specimens of oxide ores were collected from the Kal-Baneh Mn deposit. 30 polished thin sections of representative ore samples were prepared for petrographic study to establish textures and mineral assemblages of the orebodies. They were investigated by transmitted and reflected light microscopy. 6 samples were analyzed by X-Ray diffraction (XRD) at the Zar Azma Company, Tehran. 13 representative ore samples were crushed by agate mortar. The chemical composition of Mn ores was determined by inductively coupled plasma mass spectrometry (ICP-MS). Results Strata-bound Mn-oxide mineralization in the Kal-Baneh deposit is hosted by radiolarian cherts from the ophiolitic complex. The main primary ore minerals are pyrolusite and braunite, with trace hausmannite and hematite. The chemical compositions of both Mn ores are given in Tables 1 and 2. Previous studies have reported that among the major oxides, Mn, Fe, Al, Ti, and Si contents are used to discriminate the origin of Mn ores (Karakus et al., 2010; Zarasvandi et al., 2013; Sasmaz et al., 2014; Maghfouri et al., 2017). Table 1 shows that the studied ore samples have Mn contents ranging from 13.18 to 51.8 wt.% (mean=39.7 wt.%), Fe from 0.17 to 2.84 wt.% (mean=0.89 wt.%), Si from 3.8 to 25.6 wt.% (mean=11.76 wt.%), and Al from 0.2 to 4.1 wt.% (mean=1.33 wt.%). All studied ores are characterized by relatively high Mn/Fe (mean=89.39) and Si/Al ratios (mean=20). ∑ REE contents of Mn-ores range from 28.1 to 96.13 ppm. The ores studied are characterized by negative Ce anomaly (0.3-0.7) and weak positive Eu anomaly (0.64-1.35). Discussion The high value of Mn/Fe can be applied as a discrimination factor between manganese deposits. For the studied ores, this ratio varies between 4.64 -290.53 (mean=89.39) and is comparable with the characteristics of hydrothermal deposits, as defined by Nicholson et al. (1997). All studied samples are characterized by relatively high Mn/Fe ratios comparable with that of hydrothermal Mn deposits, as fractionation of Mn and Fe during hydrothermal transport and mineralization (Xie et al., 2013). Si/Al ratios of the studied samples range from 2.15 to 102.5 (mean= 20) and are comparable to those of hydrothermal exhalative Mn deposits (Sasmaz et al., 2014; Wu et al., 2016). The chemical composition of Mn ore samples compared with different types of Mn deposits in the diagrams of Si-Al (Choi and Hariya, 1992), (Co+Ni)-(As+Cu+Pb+V+Zn) (Nicholson, 1992), Co-Ni-Zn (Choi and Hariya, 1992), Fe-Mn-(Ni + Co + Cu) ×10 (Hein et al., 1994), Ce-Zr (Vereshchagin et al., 2019), Ce-(Co + Ni + Cu)/1000 and (Ce/Ce*)n-Nd (Sasmaz et al., 2020) are similar to those of hydrothermal Mn deposits. The REE patterns in the oxide ores from the Kal-Baneh deposit are similar to hydrothermal Mn deposits. The total REE (ΣREE) contents in the studied samples vary from 28.1 to 96.13 ppm and are characterized by the relative enrichment of LREE/ HREE ratios (Table 2). The low REE contents of ore samples from the Kal-Baneh deposit is compared with hydrothermal Mn deposits (Xie et al., 2013). The Ce/Ce* and Eu/Eu*values of Mn oxide ores collected from the study deposit vary from 0.3 to 0.7 and 0.64 to 1.35, respectively. Negative Ce anomaly is the most common characteristic of hydrothermal manganese deposits (Bau et al., 2014). The Mn ore samples have negative Ce anomalies within the Kal-Baneh deposit. The Eu anomalies depend on the temperature of the hydrothermal fluids and the proximity to the hydrothermal source. Large positive Eu anomalies are recognized in high-temperature (> 250 °C) hydrothermal systems at mid-ocean ridges and back-arc spreading centers (Bau and Dulski, 1996; Bau and Dulski, 1999). Some evidence such as negative Ce anomaly, weak positive Eu anomaly, absence of Fe minerals, and high value of Mn/Fe ratios in the Kal-Baneh deposit support a distal source for the hydrothermal exhalations that are contributions ofboth hydrothermal and hydrogenous processes.
Keywords
