Siirt Madenköy’s massive sulfide deposit is located in South-Eastern Turkey, approximately 45 km northeast of the historic provincial town of Siirt (Figure 1), an important oil province in Turkey, with traces of ancient Upper Mesopotamian civilizations such as Assyrians, Urarteans, Persians and Ayyubids. The deposit can be reached from Siirt via a country road. The nearest railway Kurtalan is about 80 km west. The main body of the deposit is located at an altitude between 770 and 1290 m NHN [1] . The area has a continental climate with adequate vegetation (rainfall 638 mm/year) and temperatures between 43˚C (July) and −20˚C (February) [2] . The population density 58 persons/km² is far below the national average (100 persons/km²). The population of the industrial poor area is predominantly active in agriculture.

The mining activities in Siirt-Madenköy reach back to antiquity [1] , but they are

not clearly documented in time. Old slag heaps and galleries occupy these activities. The first contemporary geological works in Siirt Madenköy were undertaken by the Institute of Mineral Research and Exploration of Turkey (MTA) in 1947. These were followed by detailed work [3] [4] [5] . In 1971, the MTA institute resumed work and described the deposit in detail for the first time [6] . This work was followed by feasibility studies [7] [8] . The mining company was only added to copper ore or concentrate in the spring of 2005.

This article thoroughly discusses the deposit for the geochemical distribution of Cu, Pb, Zn, Fe (as Fe₃O₄) and S components in order to gain new insights into their occurrence in the deposit, to assist in previous geological investigations, and to provide guidance on future work. For this the frequency distribution, correlation analysis and variogram calculation are used. Subsequently, a stock calculation is carried out by profile method in order to determine important economic parameters of the deposit. It should be noted that the data after commissioning of the deposit in 2005 were not included in this work. These are the subject of further research work, as they are predominantly relevant to the determination of reserves (see “Reserve calculation”) and this study was already completed.

The Siirt Madenköy region is located between metamorphic Bitlis massif in the north and marginal folds of the Arabian plate in the south. It consists of north-south Palaeozoic metamorphic rocks (mica schist and marbles), ophiolithic rocks of the Upper Cretaceous (peridotites, volcanic and mudstones) and the Miocene marginal folds of the Arabian plate (conglomerates and sandstones) [9] . The boundaries between these series are always given by east-west almost parallel thrust tracks, which characterize the actual tectonics (see also [10] [11] ). The ophiolithic series, also known as the South-East Anatolian Ophiolithic Belt, can be traced over a distance of about 700 km, from Hatay in the west to the Hakkarı on the Iranian border in the east. This series is regarded as the eastern continuation of the Cypriot Troodos massif and its raw material potential equalled with that of the Andes [12] . It contains numerous massive sulfide deposits of the type Cyprus, of which Helezor and Ergani-Maden in Elazığ, Mizak and Karadere in Diyarbakır and Siirt Madenköy in Siirt are the most important [13] [14] [15] [16] [17] . The formation of these deposits is associated with alpine orogeny [18] , while [19] compares these with recent occurrences of mid-ocean ridges.

The geology of the Siirt Madenköy deposit, as noted above, has rock series of two distinct sequences: these are Permian marbles of the Bitlis massif and spilite, diabase and mudstones of the ophiolitic series of alpine orogeny. This structure is called a tectonic window [20] .

The most common rocks of the deposit area are spilites, olivine pyroxenitic basalts, which occur mainly in the eastern and southeastern areas (Figure 2). They represent the oldest rock unit of the deposit, which are placed in the middle Eocene [8] . This greenish black, very fragile unit reaches a width of 450 m and is often interspersed with diabase veins. They are subdivided into dark and porphyritic (spotty) spilites [8] , which merge into each other. In the center of the unit they lead heavily altered pillow lava, which reach a diameter of 2.50 m. They sweep northeast-southwest and drop northwest at 50˚ - 60˚. Their contact with the other rock series is mostly determined by fractions. Their gas chambers are filled with calcite, quartz and zeolite. The well-developed alteration consists primarily of solidification, chloritization and sericitization. The mineralization is bound to these altered rock areas [8] [21] .

The spilites show a clear almond structure and ophiolitic or diabase-like texture under microscope [8] [20] . Their mineralogical composition consists mainly of slightly albitized and rarely idiomorphic plagioclases, as well as augite and mafic minerals such as magnetite, which is rare. The mafic minerals are mostly chloritized or sericitized. Their important secondary minerals are leucoxene and indingist.

Diabase occurs very rarely in the study area as passages in spilites and is younger. The surface diabase flows are mostly concentrated in the north and in the center of the deposit area (Figure 2). Their color changes from dark green to light green according to the degree of kaolinization or propylitization (see also [8] ). They show a granular structure. Mineralogical they consist mainly of albite and augite. Incidentally, magnetite, hematite, rutile, ilmenite and quartz also occur.

In the west and northwest of the deposit area conglomerates are common. They are not graded [22] and show no stratification. Their transition to the neighboring rocks, for example to the mudstones, is gradual. In upper areas they carry volcanic pebbles, while in the lower areas they have recrystallised pebbles with round grains of pyrite and chalcopyrite. They carry fossils of Nimmulites sp and put them in Lutetium [8] .

The north-westerly piles (scree) form the youngest rock formation in the deposit. It consists of a mixture of the surrounding rock series and reaches at most a few m thicknesses. In addition, there are still mudstones, which occur in the form of thin horizons and predominantly appear in the north (see also [7] and [23] ). In addition, gypsum and breccia horizons can be observed in places.

In the Siirt Madenköy deposit, numerous perturbations of various dimensions and properties have emerged [8] (Figure 2). Here, the northwest-southeast interference extending, which are considered as a result of vertical fractures and block movements outweigh. These movements have largely led to the shift of the geological formations and the mineralization zones. In particular, the areas of the conglomerates have been subjected to strong local reductions. The terrain observations show that the fractures were created only after the mineralization.

The mineralization in Siirt Madenköy is bound to the spilites according to [6] and [8] , which have massive flow structures and lead cushion lava. These are particularly evident in the southwest of the deposit (Figure 2). The ore outbreaks are largely altered.

The mineralization in Siirt Madenköy constitutes a lenticular ore body extending northeast-southwest, consisting of numerous individual lenses of different dimensions at approximately 50˚ to the northwest (section A-A' of Figure 2 and Figure 10). The total thickness of the ore body reaches about 150 m. Its length is about 700 m, while its width varies between 100 and 300 m. In the ore body is a significant vertical zoning to determine. From the bottom (magnetite) to the top (pyrite), the following resource zones are similar, similar to those of the Cyprus type massive sulfide deposits:

Pyrite,

Pyrite + chalcopyrite,

Pyrite + chalcopyrite + sphalerite,

Pyrite + chalcopyrite + magnetite,

Magnetite.

Pyrite is more or less everywhere, while magnetite occurs only in the deeper part of the mineralization. This indicates a primary depth difference characteristic of hydrothermal deposits, as indicated by [24] and [25] . The alteration of ore grades according to the depth in a deposit is an old fact of experience that some elements, such as Zn, increase in depth, or vice versa, such as Pb and Ag, which is why in old Pb mining, the occurrence of sphalerite as a “mining end” was viewed. This change in element contents with depth is interpreted as a consequence of the occurrence of higher temperature zones.

It is already macroscopically, without taking into account their genesis, to distinguish clearly massive, storied and impregnated mineralization. Of central importance is the massive mineralization common in lower areas of the deposit [6] [8] . It is composed of almost pure pyrite, chalcopyrite or magnetite or all of them. Their metal contents are highly variable depending on the composition of the ore, so that in places 16% Cu, 48% S or 92% Fe₃O₄ reach (see Table 1). This ore is often surrounded by all-over ore impregnation, which consists of randomly distributed single ore minerals and low metal contents lead. This type of ore predominantly consists of chalcopyrite [8] and fills in places cracks and crevices of country rock, which results in the net-like stock work mineralization. This intersperses both types of ore and occurs mainly in the lower areas of the ore zone, which is typical for volcanic massive sulfide deposits.

The mineralogical composition of these ore grades is identical, and generally consists of sulfidic ore minerals. Pyrite is the most widely used sulfidic mineral with grain sizes of 2 - 3 mm [20] . It is predominantly idiomorphic or hypidiomorphic, showing cataclastic texture and colloidal structure (Figure 3). Its cracks are filled with gangue minerals and are older than chalcopyrite, sphalerite

*Fe analysed as magnetite (Fe₃O₄).

and magnetite. He leads ilmenite and magnetite inclusions in places [8] . Occasionally pyrite from converted pyrrhotite can also be observed.

Magnetite is the second most abundant mineral after pyrite and increases in depth to pure magnetite (see Figure 6(a)). It is mainly idiomorphic or hypidiomorphic with pyrite and chalcopyrite. Its grain sizes reach a diameter of 0.30 mm. Rarely does he appears as a lamb. At margins he is often martitized or rarely converted into leucoxene. Its ilmenite, rutile and pyrrhotite inclusions are common [20] .

With pyrite and magnetite, cataclastic copper gravel also occurs (Figure 3). It is fine-grained, marginally limonitized, shows chalcocit and coveline transitions. Occasionally, sphalerite inclusions can be seen. Incidentally, numerous other oxides, hydroxides, sulphates and carbonates can be found. These are mainly sphalerite, galena, marcasite, pyrrhotite, bornite, coveline, chalcocite, linseed and Fahlerz. Quartz, chlorite, barite, siderite and carbonates must be listed as gangues [6] [20] .

Mineralogical investigation methods are not sufficient to separate Cu ores of different origin from each other with sufficient accuracy. For this reason, geochemical investigation methods are used in addition.

The chemical composition of the ores is of particular importance for the valuation of a deposit. It can give important clues to its genesis, facilitate the processing of the ores and gain valuable elements. An overview of the chemistry of the ores of Siirt Madenköy, compared to the similar deposit Ergani-Maden, is given in Table 2.

The geochemical analyses of copper ore samples from the Siirt Madenköy deposit show a moderate degree of mineralization, averaging 1.33% Cu (Table 1). The contents of all main elements vary very much. The high levels of FeO (31.83%) and SO₃ (27.62%) indicate high magnetite and pyrite concentrations. Na does not appear in any of the investigated ore samples in clearly detectable concentrations, while K has been detected in only 2 samples. Also Ca and Mg are very impoverished. This may be related to the basic character of the rocks and

¹Total ironoxide as FeO; ²bdl: Below dedection limit.

the hydrothermal alteration. The concentrations of valuable materials, such as those of Ag, Pb and Zn are very low, which is also to be expected due to the rarity of galena and sphalerite. In general, Siirt Madenköy’s Cu ores are poor in trace elements. Significantly high enrichments in relation to their Clarke values show Bi (217 times), Co (13 times), Cu (241 times), Mo (50 times), and Se (363 times), with As (0.16%) and Ba (10, 25%) sometimes reach high concentrations (Table 2). The high fluctuations of the components are due to the different types of ore.

Numerous minor and trace elements can be replaced by the predominant minerals such as pyrite, chalcopyrite, magnetic gravel, galena, sphalerite and magnetite. The determination of the actual concentrations of the investigated trace elements in the individual mineral phases requires single-mineral analyses, which will be the subject of further research.

There is no significant relationship between SiO₂ contents and the contents of the main components or trace elements analysed (Table 2). The concentration of the plurality of elements is opposite to that of the SiO₂. This means the displacement of the silicates by sulfide or oxides. In contrast, MgO, TiO₂, Ni, and V show a marked dependence on Al₂O₃, which is related to the diadochiene relationships between these elements in pyroxenes and mica. Despite the distribution of chalcopyrite and pyrite, FeO has no clear relation to Cu and SO₃, which can be explained by different modal conditions of magnetite, pyrite and chalcopyrite. However, Cu and SO₃ levels are parallel to each other and to those of Co and Se. This means that Cu, Co, and Se are chalkophilically bound and that Se has largely replaced S. In addition, contents of Ba, Pb and Sr are significantly related due to the similar ionic radii (0.137, 0.124 and 0.112 nm) and diadochiene relationships and indicate their hydrothermal origin.

Also, the ratios of certain oxides or elements provide important information. For example, the FeO/TiO₂ ratio of about 127 for basic rocks is high, possibly related to hydrothermal alteration, that is, Ti removal. The ratio of Cu to Ni (633) is extremely high compared to that of the magmatic sulfide deposits of basic rocks (about 10) [28] . In contrast, that of Cu/S (0.12) is lower, suggesting pyritic power.

The comparison of the average analytical values of the Siirt Madenköy copper ore samples with those of the Ergani-Maden deposit shows a certain similarity of both deposits (Table 2). For example, the concentrations of Cu, FeO and SO₃ are very high. The deposit Siirt Madenköy is compared to Ergani-Maden Cu poorer (see also [8] ). The higher FeO and SO₃ contents in Siirt Madenköy indicate rich magnetite or pyrite mineralization, leading to low levels of SiO₂, Al₂O₃ and MgO. The ores of Siirt Madenköy, on the other hand, contain numerous trace elements such as As, Ba, Bi, Mo, Pb, Se and Zn in higher concentrations than Ergani-Maden (compare [29] ).

Massive sulfide deposits can be classified with special features in mind [30] . These are, for example, metal contents, age and country rock type. Also, the method of the Cu ratio (CR = 100Cu/(Cu + Zn)) and the Zn ratio (ZR = 100 Zn/(Zn + Pb)) is an important definition factor for distinguishing types of deposits such as Cu and Zn types [31] . Since it starts from metal contents, it is often used. At the Siirt Madenköy deposit, this factor indicates an average of 79 Cu and 81 Zn ratios for a Cu type Siirt Madenköy deposit (Cu ratios = CR > 60), as shown by [32] . These values are indicative of Cyprus type massive sulfide deposits and indicate saturation of the ore resolutions at Cu and Zn. For Siirt Madenköy this means, for example, the Zn saturation of the pyrites and the chlorides by the hydrothermal alteration. This is the case for the low-Pb massive sulfide deposits of the Cyprus type [31] .

The distributions of the mean values of Cu, Pb, Zn and Fe of the forty-nine core drillings are shown in the concentration triangles of Figure 4(a) and Figure 4(b). It can be seen that Cu is most concentrated relative to Pb and Zn (Figure 4(a)), while the Pb/Zn ratios remain approximately the same. As a result, the Siirt Madenköy deposit, as defined by [33] , is assigned to the Cu type of bulk sulfide deposits, which is consistent with the result of the Cu ratio [32] . This is associated with the ophiolitic country rocks of the Cyprus type massive sulfide deposits [34] , as indicated by [17] and suggesting very low levels of TiO₂ and P₂O₅ as an indication of mid-ocean ridges. Hereby, a Co/Ni ratio of 0.29 to 1.97 is emphasized for massive sulfide deposits with serpentinitic country rocks and for those with basaltic values of 1.09 to 8 [35] . This ratio is between 6.7 and 44 in Siirt Madenköy in the analysed ore samples, which is much higher.

Figure 4(b) shows the ratio of oxidic (e.g. magnetite) and sulfidic ores (e.g. pyrite and chalcopyrite), so that the average contents of Cu, Fe₃O₄, and pyrite in the wells are very different. This reflects the distribution of rich local ore concentrations and poor ore or impregnation ores. This also illustrates the supremacy of the S over Cu and Fe₃O₄ (ignoring the non-magnetic Fe), where S has low scattering, which means extensive or relatively regular occurrence of the sulfidic ores (not shown, see Figures 7(b) and [32] ). Terrain observations, mineralogical composition of the ores and the microscopic findings, such as those of Figure 3, also support these views.

The Figure 5 shows the position of the deposit Siirt Madenköy in the Cu-10Pb-Zn triangle according to [36] . In it are shown for comparison recent mineralization from the different oceanic environments. It can be seen that the massive sulfide deposit Siirt Madenköy is characterized by average Cu/10Pb and Cu/Zn ratios. The location of the representative point (SM) shows the area of the Cu class of massive sulfide deposits [30] . This can be achieved, for example, with the mineralization of the Galapagos Spreading Center (GAL), the Middle Oceanic Ridge (MOR), the Ergani-Maden (EM) and Küre (Mağaradoruk, KM) massive

sulfide deposit, but with relatively higher Pb-Zn. Maintain, compare, and differ significantly from the Kuroko deposits (back-arc basin). As a result, the Siirt Madenköy deposit is considered to be one of the slow-spreading ridges massive sulfide deposits [37] . This is also supported by the elemental contents of Table 2 (see [28] ).