First report of Geochemical Characteristics of the Sangan Manganese Occurrence, Northeast Khash (Iran)

The Sangan manganese deposit is located 28 km northeast of the Khash city (Southeast of Taftan volcano) in the Sistan & Baluchistan province. Structurally and lithologically, this deposit lies in the central part of Iranian flysch zone. The ore body is layer in shape and lies above the Shale with intercalation meta sandstone lithic tuffs of the Quaternary volcanic units contact and is completely hosted within dark gray to black lithic tuffs and in places interlinks with the dark gray to black lithic tuffs, so that the lithic tuffs play role keybed (line exploration) of manganese ore in the region. The geochemistry characteristics of the Sangan deposit was studied by means of major oxide, trace and Rare Earth Element (REE) contents and the origin of mineralization was discussed. The relatively high Al concentrations (5.95 to 7.22 wt.%, average = 6.61) in the ore of Sangan Mn deposit might result from lithic tuffs, which are the host rocks of the ore. Low titanium values (0.24 to 0.36 wt.%, average = 0.31) indicate limited clastic material entry during mineralization. In chondrite normalized REE graphics in all ore samples were characterized by slight negative Ce (0.10 to 0.11, average = 0.11) and negative Eu (0.18 to 0.22, average = 0.20) anomalies. The negative Ce anomaly was typical to hydrothermal deposits and negative Eu anomaly indicates contamination from the continental crust and or sediment contribution via dehydration. The available data like; Mn:Fe (average 4.07), relatively high Ba (average 508,50), Co:Ni (average 0.18), Co:Zn (average 0.34), total REE (average 117.94), LREE > HREE, LREE:HREE (average 10.33), La:Ce (average 0.56), slight negative Ce and Eu anomalies and discrimination diagrams for Mn deposits indicated that the Sangan manganese deposit is hydrothermal type volcano-hydrothermal mineralization.


Introduction
A variety of features of manganese deposits, such as geochemistry, distribution, composition, and their formation environments are considered in many of publications 1 . It is now generally understood that manganese deposits have diverse origins. They can be formed by various processes, including sedimentary, hydrothermal, hydrogenous, and super gene. Hydrothermal manganese deposits are smaller than sedimentary manganese deposits 2 . Hydrothermal manganese deposits are directly precipitated from low temperature hydrothermal solutions 3 . These deposits are generally of laminated and strata bound or occur as irregular bodies and epithermal veins. They are formed in different tectonic settings, such as the marine environment next to spreading centers, intraplate seamounts, or in subduction related island arc settings, and are found in both modern and ancient geologic environments 4,5 . Hydrothermal deposits are characterized by high Mn:Fe content and low trace metal concentrations 6,7 . Manganese and ferromanganese ore deposits are recognized with different ages and geologic settings in Iran 8 . For example, the Infracambrian Narigan Mn ore deposit in Yazd province (Central Iran) has a volcano-exhalative genesis. The Cretaceous Benvid Mn deposit 35 Km south of Nain-Isfahan, with possible sedex genesis and Kamar Talar Mn deposit in Sistan suture zone, East Iran 9 . There has been no detailed investigation powders under 200 meshes were analyzed at Kansaran Binaloud Laboratories, Tehran, Iran. Major oxide and trace element contents were determined with XRF and ICP-OES Respectively. REE's were analyzed with ICP-MS method. Results of analysis are given in Tables 1, 2 and 3. on the origin of the Mn mineralization from the Sangan area. Therefore, the purpose of this paper is to discuss field observations in conjunction with major, trace, and rare earth element (REE) geochemical data to constrain the genesis of Mn ore deposit in the Sangan region, Southeastern Iran.

Geological Setting
The Iran plate is part of northern margin of Gondwana which is separated from Eurasia by the paleotethys Ocean. The movement of bloks along folds and tectonic force are the main factors which played prominent roles in shaping the structural characteristics and geology of Iran. The Pressures and Strains to the Iran plate caused the region to be classified based on different theories in to several tectonic units [10][11][12][13][14][15] . The studied area is located in the central part of Iranian flysch zone. This zone is located between Lut Block to the west and Helmand (in Afghanistan) to the east. In contrast to Lut Block, the Flysch Zone is highly deformed and tectonized and consists of thick deep-sea sediments like argillaceous and silicic shales, radiolarite, and pelagic limestone and volcanic rocks such as basalt, spilitic basalt, diabase, andesite, dacite, rhyolite, and subordinate serpentinized ultramafic rocks. The basement is likely composed of an oceanic crust. Most rock units in this zone fall into three main groups: 1-Flyschoid sediments, 2-Volcanic, volcano sedimentary and intrusive rocks 3-Ophiolitic series 16 . However there are some other names of this zone such as Nehbandan-khash zone 17 , Zabol-Baluch zone 13 , Flyschzone 18 Sistan suture zone 19 , Iran East mountain 20 . The Sangan manganese Occurrence is Located 28 km Northeast of Khash city (Southeast of Taftan volcano) and 1 km West of Sangan village (N28-31-9.3, E61-15-42.3). Based on the Geological Map (1:1000 Scale), the Most Important Rock unites around deposit consists of gray to light green shale with intercalation meta sandstone, Dark gray to black lithic tuffs, white to milky ignimbrite tuffs and recent alluvium. Manganese Mineralization is associated with dark gray to black lithic tuffs within Quaternary volcanic units (Figure 1 A, B and Figure 2).

Materials and Method
10 ore samples (~500 g each) were collected systematically from the Sangan manganese deposit. All this ore samples for geochemical analyses were taken representatively from the surface outcrop of ore beds in different locations. Samples

Field Observations
The ore body in the study area is layer in shape. The ore body lies above the Shale with intercalation meta sandstone-lithic tuffs contact and is completely hosted within dark gray to black lithic tuffs and in places interlinks with the dark gray to black lithic tuffs, so that the lithic tuffs play role keybed (line exploration) of manganese ore in the region. Wherever we have this rock unit (lithic tuffs), manganese mineralization could be observed as scattered grains in the space between ashes and pyroclastic particles. But, these pyroclastic particles have been crashed in some places and there have been some fine fractures between them that they are also filled with manganese oxide ores result from volcanic activities. The ore layers generally vary in thickness from 1 to 2 m, in length from 400 to 800 m and wide from 4 to 8 m. The ore trends approximately eastwest to northwest-southeast and dips southeast between 20° and 25°. Ore has been exploited mainly by small-scale miners using rudimentary methods at Sangan (Figure 3).

Major and Trace Elements Geochemistry
Geochemical criteria to distinguish ferromanganese deposits of various origins are well established. Major element ratios, trace element concentrations have been widely used to assess the origin of manganese deposits [21][22][23] . Among the major oxides, Mn, Fe, Ti and Al contents are very useful to delineate the origin of manganese ores 23,24 . Many authors use Mn:Fe ratio as discrimination genetic factor between manganese deposits; for example; this ratio in lacustrine deposits is (Mn:Fe< 1), hydrogenous (Mn:Fe = 1) and Sedex deposits (0.1 <Mn:Fe< 10) 25 . Analytical results of the major and trace elements of the Sangan Mn deposit are given in Tables  Ba concentrations in hydrothermal solutions are higher than seawater because of the influence of volcanic activity and sedimentation 28,33,34 . Ba concentrations in the Sangan manganese deposit range from 456 to 560 ppm (average = 508.50) reflecting in general, the characteristics of hydrothermal deposits.
Different major and trace element discrimination diagrams have been proposed by many workers to distinguish manganese ores of various origins 26,29,30,[35][36][37][38][39][40][41] . These discrimination diagrams have been used to distinguish between a hydrothermal (continental or marine) and a hydrogenous origin. The term hydrothermal refers to manganese oxides deposited directly from geothermal waters around hot springs and pools in continental environments or sedimentary-exhalative manganese mineralization deposited in marine environments 38 . The term hydrogenous refers to deposits formed by slow precipitation or adsorption of dissolved components from sea water 26,36,38 . The Si vs. Al binary diagram 30,39 , the Mn-Fe-(Co + Ni + Cu) × 10 triangular diagram 26,36,41 , the Zn-Ni-Co triangular diagram 29 , the Co:Zn vs. Co + Ni + Cu diagram 30 , and the Co + Ni vs. As + Mo + V + Cu + Pb + Zn diagram 37 are used in this study to discriminate between the hydrothermal and hydrogenous character of the deposit.
All the studied manganese ore samples in triangular ( Figure 4B and C) and binary ( Figure 4A, D and E) discrimination diagrams plot within the hydrothermal field. Trace element concentrations in the manganese oxides show the mostly hydrothermal origin for manganese deposit in the Sangan region (Table 2; Figure 4A to E).

Rare Earth Elements Geochemistry
Major oxide, trace and REE geochemistry are very useful for understanding the formation conditions of ore deposit. REE contents of 8 ore samples collected from the Sangan manganese deposit are listed in Table 3. Hydrothermal deposits show relatively low REE, but hydrogenous deposits have a significantly higher amount 28,[42][43][44] . The total REE (ΣREE) concentrations of Sangan Mn ore range from 108.64 to 130.94 ppm (average = 117.94) (Table 3), the low contents of REE composition of studied ore samples are conformable with hydrothermal manganese deposits 23,45 . Total light REE: heavy REE (i.e., ΣLREE:ΣHREE) and La:Ce ratios of the Sangan Mn ore given in Table 3, can be used as an indicator of primary enrichment during the Mn oxidation processes 28,33,46 . LREE > HREE value may indicate mineralization related to hydrothermal First report of Geochemical Characteristics of the Sangan Manganese Occurrence, Northeast Khash (Iran) solutions 28,33,47 . The total LREE: total HREE ratio ranges from 9.64 to 11.19 (average = 10.33) in the Sangan Mn ore. These values indicate that hydrothermal solutions played an important role in the formation of Sangan Mn deposit. Hydrothermal crusts have La:Ce ratios similar to seawater (~2.8), but hydrogenous Mn-Fe crusts have a much lower La:Ce ratio (~0.25) 48 . La:Ce ratio for the Sangan Mn ore vary between 0.51 and 0.61 (average 0.56) (Table 3 and Figure 5). This ratio suggests a major input from a hydrothermal source for the Sangan Mn ore Figure 5.
Although the relationship between manganese deposits and their REE distribution has been studied [49][50][51][52] , there is no generally accepted model for reflecting the deposit type (e.g., hydrothermal, diaganetic, hydrogenetic) and oxidative and reductive deposition conditions. Ce and Eu, the two most important REEs, are commonly used for the prediction of fluid source and redox potential of the environment. Ce and Eu anomalies are defined as Ce:Ce* = [(Ce n ):(La n ×Pr n ) 1/2 and Eu:Eu* = [(Eu n ):(Sm n ×Gd n ) 1/2 , respectively, where Ce* and Eu* are the hypothetical concentrations 53 . The subscript "n" indicates chondrite-normalized values 54 .
Slight negative Ce anomalies are considered as an indicator of volcanogenic input 55 or hydrothermal contributions to seawater 50,51 , whereas a strong negative Ce anomaly is characteristic of low temperature hydrothermal deposits around the hot spots in mid-ocean and island arc spreading centers 56,57 .
Positive Ce anomalies are characteristic for modern seafloor oxyhydroxide deposits and nodules 58 . A negative Ce anomaly is observed in all ore samples taken from the Sangan Mn ore (Table 3). Ce:Ce* anomaly values range between 0.10 and 0.11 (average = 0.11) a range which is similar to low temperature hydrothermal deposits.
A positive Eu anomaly in hydrothermal deposits suggests high temperature hydrothermal fluids 59 and reflects the interaction of heated waters with substrate volcanic rocks of high Eu content during circulation 60 . A negative Eu anomaly indicates an insufficient interaction of ground water with substrate volcanic rocks due to low temperature 60 and contamination from the continental crust and or sediment contribution via dehydration 28,33,61 .
A negative Eu anomaly is found in all the manganese samples taken from the Sangan Mn ore (Table 3). Eu:Eu* anomaly values range from 0.18 to 0.22 (average = 0.20). This suggests a low temperature hydrothermal solution, which affected mineralization. We conclude that REE patterns of the Sangan manganese deposit are generally similar to those from hydrothermal manganese deposits.
All the studied ore samples shows light negative Ce and negative Eu anomalies ( Figure 6).
REE patterns of the region ( Figure 6) are compared with those of hydrothermal and hydrogenous manganese deposits (Figure 7). Results indicate that hydrogenous  manganese deposits are more enriched in REE's than their hydrothermal equivalents and hydrogenous manganese deposits are represented by positive Ce anomaly, but hydrothermal deposits are characterized by negative Ce anomalies 3,62 . Ore samples of the Sangan manganese deposit show slight negative Ce anomalies which resemble the pattern of hydrothermal deposits ( Figure 6). Eu shows negative anomaly in all ore samples indicating contamination from the continental crust and or sediment contribution via dehydration 33,61 .

Conclusions
The Sangan manganese deposit is associated with Dark gray to black lithic tuffs within Quaternary volcanic units at 28 km Northeast of Khash city (Southeast of Taftan volcano) and 1 km West of Sangan village (N28-31-9.3, E61-15-42.3). Major oxide, trace and REE element assessment show that hydrothermal activities were effective for the formation of the Sangan manganese deposit. Also, the studies reveal that mineralization of manganese in layered form and strati form and related to Dark gray to black lithic tuffs with quaternary age, which is generally conformable with bedding host rock (lithic tuffs). The contacts with the tuffs are suddenly and associated with pyroclastic-volcanic activities of Taftan volcano. They have been formed as the horizontal layers and placed on the middle Eocene folded flysches unconformably. Therefore, it can be concluded that both volcanic and hydrothermal conditions were caused in the formation of Sangan manganese deposit which may be described as related to volcano-hydrothermal occurrence. It seems that hydrothermal fluids and volatile materials with high hydraulic pressure and explosively are ejected and exited from a further volcanic source related to Taftan Volcanism and have passed distance due to the low density and gradually have been deposited as horizontally and unconformably on the middle Eocene flysches. The question is why they have been found in only one horizon and contaminated with manganese oxides. Manganese along with other materials such as volcanic ashes and pyroclastic fragments during the exit of the volcanic channel do not react with oxygen at the same time, because Manganese has low ionic potential, it takes a short time, which coincided with an explosion of volcanic ashes and pyroclastic fragments and finally it's deposition. In the case of fine-grained material impregnated with manganese oxy-hydroxides are deposited with volcanic ashes and angular fragments of pyroclastic simultaneously, and finally, they have made a cycle of manganese mineralization horizontally.