Genesis of Ferromanganese Deposits from the Central Anatolian Province, Yozgat-Aşağı Eğerci Village-TURKEY: Geochemical Properties and Fluid Inclusions

Eğerci village is located 16 km southwest of Yerköy (Yozgat) area which has a ferromanganese deposit that formed at the contact between basalt and limestone and shows that a banded stockwork structure occurs occasionally within the limestone. The mineralization consists of pyrolusite, goethite, and ramsdellite, together with a lesser quantity of magnetite. Gangue minerals are determined as calcite and quartz. REE data from the mineral samples demonstrate a range from 2.70 63.70 ppm and the average value is 28.00. These results permit a comparison to be made with mineralization in hydrothermal deposits. Moreover, mineral samples show a positive Eu anomaly 0.88-48.10 ppm (ave. 9.94 ppm). The Ce anomaly values vary between 0.02 and 0.88 ppm (ave. 0.58 ppm). It is possible that the mineralization may be affected by the mixing of seawater and hydrothermal fluids. The value of the positive Eu anomaly is evidence of modern oceanic hydrothermal manganese deposits. Insight of previous fluid inclusion, studies can be easily inferred that mineralization can occur at three different stages. The temperature of the first stage ranged from 338 oC to 428 oC and other stages vary from 269 oC 317 oC and 143 oC 236 oC, respectively. As a comparison, calculated salinity is higher in Type I fluid inclusions (1.9-14.7 wt.% NaCl equiv.) than Type II and III fluid inclusions (1.9-5.1 wt.%NaCl equiv.) It is possible that the mineralization was formed by the mixing of magmatic and meteoric waters. genesis,­wall­rocks,­the­sources­of­different­hydrothermal­fluids­ in­the­mineralization­with­ore­REE­geochemistry,­and­fluid­inclusion studies and to determine a mineralization model for ore deposits in the region. 2. GEOLOGICAL SETTING 2.1. Regional Geology The manganese mineralization which forms the topic of the study is­observed­in­Aşağı­Eğerci­village­located­16­km­southwest­of­ Yerköy (YOZGAT) county and is situated within one of the most important massifs in Turkey of the Central Anatolian massif. The oldest­unit­outcropping­in­the­region­is­the­Paleozoic­Bozçaldağ­ Formation (Fig. 1). The unit named by SEYMEN (1982) comprises grey coloured, mostly coarse calcite crystal-rich, moderately-thick bedded marbles, and massive marbles. The massive marbles­are­observed­in­a­very­small­area­south­of­Hacılı­village­ in the study area and are cut by an Upper Cretaceous Central Anatolian­granite­(AKÇAY­et­al.,­2007).­The­Eocene­Boğazköy­ Formation (ÖZCAN et al., 1980) transgressively overlies intrusives in some regions and older units above an angular unconformity in other regions in the study area and close surroundings. The unit has volcanic interlayers and comprises sandstone, siltstone, some pebblestone, mudstone, and limestone. This formation is divided into three members of the ‘limestone member’ comprising sandy-silty limestone and massive limestone containing­nummulites,­corals­and­gastropod­fossils,­the­‘Alimpınar­volcanic member’ comprising basalt and basaltic pyroclastic rocks, and­the­‘dacite­member’­comprising­dominantly­dacitic­tuffs­with­ occasional dacitic and rhyolitic rocks (ÖZCAN et al., 1980). The dacite member is not observed in the study area. These three Article history: Manuscript received May 20, 2021 Revised manuscript accepted September 10, 2021 Available online October 27, 2021


INTRODUCTION
Manganese deposits in Turkey are divided into four main groups by noting sources, tectonic environments, and structural features (ÖZTÜRK, 1993). These are; 1. Hydrothermal and hydrogenous manganese deposits within radiolarite cherts, 2. Diagenetic deposits related to black shales within Lower Cretaceous carbonates, 3. Hydrothermal deposits within volcano-sedimentary and 4. Sedimentary-derived deposits within Oligocene sediments.
Many manganese formations are observed along a line from west to east in Yozgat province. Most of these are emplaced within ophiolitic units widely observed in the region and are manganese-ferromanganese deposits interlayered with radiolarites. Though some deposits were determined to have very high grades (up to 69.91%), they remain short-term operations due to low reserves. While Si values reach up to 40% in some regions, the Fe content values reach up to 29% (ÖKSÜZ 2011a,b;ÖKSÜZ & OKUYUCU, 2014;ÖKSÜZ, 2018;ÖKSÜZ et al., 2021). The geological, mineralogical, and geochemical assessments of these formations have been the topic of many studies (ÖKSÜZ, 2011a,b;ÖKSÜZ & OKUYUCU, 2014;ÖKSÜZ, 2018;ÖKSÜZ et al., 2021). In those studies, it was determined that Yozgat manganese depositshavethreedifferentoriginsofhydrothermal,hydro genous, and detrital sources.
The topic of the study is the ferromanganese mineralization observedintheEğerciregion,whichwasobservedtobedifferent from other mineralization in the Yozgat region. This ferromanganese deposit in the region was selected as the research topic as it has not appeared in any previous studies. The basic aims of thestudyweretodefinethegeologyoftheregion,theorepara genesis,wallrocks,thesourcesofdifferenthydrothermalfluids inthemineralizationwithoreREEgeochemistry,andfluidinclusion studies and to determine a mineralization model for ore deposits in the region.

Regional Geology
The manganese mineralization which forms the topic of the study isobservedinAşağıEğercivillagelocated16kmsouthwestof Yerköy (YOZGAT) county and is situated within one of the most important massifs in Turkey of the Central Anatolian massif. The oldestunitoutcroppingintheregionisthePaleozoicBozçaldağ Formation (Fig. 1). The unit named by SEYMEN (1982) comprises grey coloured, mostly coarse calcite crystal-rich, moderately-thick bedded marbles, and massive marbles. The massive marblesareobservedinaverysmallareasouthofHacılıvillage in the study area and are cut by an Upper Cretaceous Central Anatoliangranite (AKÇAYetal.,2007).TheEoceneBoğazköy Formation (ÖZCAN et al., 1980) transgressively overlies intrusives in some regions and older units above an angular unconformity in other regions in the study area and close surroundings. The unit has volcanic interlayers and comprises sandstone, siltstone, some pebblestone, mudstone, and limestone. This formation is divided into three members of the 'limestone member' comprising sandy-silty limestone and massive limestone containingnummulites,coralsandgastropodfossils,the'Alimpınarvolcanic member' comprising basalt and basaltic pyroclastic rocks, andthe'dacitemember'comprisingdominantlydacitictuffswith occasional dacitic and rhyolitic rocks (ÖZCAN et al., 1980). The dacite member is not observed in the study area. These three membersidentifiedintheformationhavebothlateralandvertical transitions with each other. Additionally, the basal structures observedintheAlimpınarvolcanicmemberindicatesubmarine volcanism. The unit is generally observed in the north-northwest andsoutheastregionsaroundAşağıEğercivillage. TheOligo-ceneİncikFormation(OKTAY,1981),isdistinguishedbydominant pebblestone, sandstone, and mudstone lithologies and formed in a terrestrial environment, while Middle Miocene-Pliocenelacustrineandterrestrialfluvialsedimentsunconformably overlie all units. The youngest unit in the region is the Quaternary alluvium (KETIN, 1955;AKÇAY et al., 2007).
Inthestudyarea,theeffectsareobservedoftheLaramian stage of Alpine orogenesis on the intense deformation of central Anatolia and the Taurus (KETIN, 1966). Magmatism covering large areas of the region occurred as plutonic activity within crystalline massifs, and submarine volcanism in the Upper Cretaceous and Middle Eocene periods. Middle Eocene units represent rocks developed in shallow marine and volcanic facies. In the Lower-Middle Eocene period, the sea level was higher than in the Cretaceous period. Towards the end of the Middle Eocene, the sea gradually began to retreat, lagoons formed, and gypsum and clayey marls formed toward the end of the Middle Eocene. At the end of the Middle Eocene, the sea regressed further and at the same time uplift and erosion occurred, with red conglomeritic units forming in the Oligocene. During the Oligocene, the sea regressed further and lagoons formed. At the end of the Oligocene, occasional fresh and saltwater lakes remained while the sea was fully regressed (KETIN, 1955). Volcanic activity in younger cycles was not observed in the study area (KETIN, 1955).

SAMPLING AND ANALYTICAL METHODS
A total of 40 ore samples were taken systematically from the ferromanganese mineralization observed in the study area. These samples were separated for geochemical analysis, polished sections,andfluidinclusionstudies.Samplepowdersunder200 mesh were analyzed at the General Directorate of Mineral Research and Exploration (MTA) in Turkey. Major oxide and trace element contents were determined with ICP-ES and REE's were analyzed with the ICP-MS method. Results of the analyses are given in Tables 1 to 3. Polished sections were prepared from 15 samples by the same unit. The polished samples were investi-gatedwithareflectedlightLeicamicroscopeinBozokUniversity Laboratory. For accuracy of ore paragenesis, 15 samples had XRD analysis performed in the Bozok University Science and Technology Application and Research Centre (BILTEM).
Forfluidinclusionanalysis,quartzandcalcitesamplesobserved as veins were examined in mineralized samples from the studyarea.Atotalof4sampleshadfluidinclusionstudiesperformed. Measurements were performed microthermometrically on double-sided polished sections, using a Linkam THMG-600 heating and cooling stage mounted on an Olympus BX51 micro-scopeintheRecepTayyipErdoğanUniversity,Departmentof GeologicalEngineering.Theequipmentwassuitableformicrothermometric measurements from -196 to 600 °C. The Linksys-32 DV program was used for measurements with 0.1 °C sensitivity and repeated measurements were shown to have an accuracy of ±0.2 °C for freezing and ±1 °C for heating experiments.
The 'limestone member' is commonly observed in the study area and comprises coral, gastropod, and lamellibranchs, grey, moderately-thickly bedded, sandy-silty limestone, and massive limestones (Fig. 2a-c). The unit is widely observed in the region and contains banded and stockwork ferromanganese formations in the study area (Fig. 2c, d-f).
TheAlimpınarvolcanicmembercomprisesbasaltandpyroclastics of basaltic composition. The unit with widespread outcrops in the study area has a lateral transition to the limestone member. Basalts with basal structures indicating submarine volcanism are a purple-black colour, with large glassy minerals, abundant fractures, and joints (Fig. 2c). Pyroclastics are lightly coloured, with uneven erosion surfaces and glass fragments (AKÇAY et al., 2007) (Fig. 2g). The unit has a broad distribution in the study area. Manganese mineralization is observed as bands and occasional stockwork at the contact with limestone and within the limestones (Fig. 2, d-f).

Ore Petrography
Polished sections of the mineralized samples were investigated withareflectedlightmicroscope.Additionally,XRDanalysis   was performed to support the mineral paragenesis (Fig. 3). Accordingly, the main minerals in the ore paragenesis were pyrolusite, goethite, and ramsdellite. Lesser amounts of magnetite wereobserved.Theganguemineralscomprisecalciteandquartz.
Pyrolusite is the most abundant manganese oxide mineral in manganesedeposits.Therearethreedifferentpolymorphsof MnO 2 . The most stable and abundant of these is pyrolusite, which is a mineral that may form in both supergene and low-temperature hydrothermal environments and does not infer meaning in terms of origin (NICHOLSON, 1992). Apart from this, other manganese minerals including ramsdellite and manganite occur in the form of replacements. Pyrolusite formation is typical with weathering developing in terrestrial environments. In this type of mineralization, pyrolusite may contain simple remnant materials from the environment during transport and pyrolusite precipitation generally occurs in carbonate rocks including limestone or dolomite (RAMDOHR, 1980). In environments with a high oxidation potential, pyrolusite may be independent of pH (KRAUSKOPF, 1989). It displays a cream and yellow colour un-derthefirstNicol,whilethereiscream,yellow,bluishgreystrong  anisotropy under the second Nicol ( Fig. 4a, b). There are three differentpyrolusitetypesinthestudyarea (Fig.4c).Oneofthese isveinfillwithsmallgrainsize (Fig.4d),whiletheotherhas larger grains in the form of foliation (Fig. 4c, e, f). Additionally, pyrolusites were observed in the form of replacements with ramsdellite ( Fig. 4e-h).
Ramsdellite is one of the naturally occurring manganese oxide polymorphs. Due its similarities with pyrolusite, it is very difficulttomakeadirectcomparison.Thoughpyrolusiteismore commonly observed, ramsdellite may be found in abundant amountsinmanganeserichenvironmentsexposedtoaqueous alteration at low temperatures (OSTWALD et al., 1984). If the two minerals form together, pyrolusite is notable for its higher sheen. Both minerals are included in the paragenesis of the other, and ramsdellite converts to pyrolusite when heated above 300 o C (RAMDOHR, 1980). This type of transformation is in the form Bluey grey, strongly anisotropic pyrolusite and orange-brown goethite with strong internal reflection (II Nicol). c. Foliation in large-grained (Py-I) and fine-grained pyrolusite (Py-II). d. Fine-grained, vein-fill pyrolusite (I Nicol), light and dark grey goethite with occasional oolite-like texture (I Nicol). e. Cream, bright yellow ramsdellite and pyrolusite were observed replacing ramsdellite (I Nicol). f. Same photograph (II Nicol). Py: pyrolusite, Gth: goethite, R: ramsdellite.    of nested or small pyrolusites observed surrounding ramsdellite inthestudyarea (Fig.4eh).RamsdelliteidentifiedwithXRDis differentiatedfrompyrolusitebyitsgreenishgreyanisotropy colo ur especially (see Fig. 3; Fig. 4f, h; Fig. 5b).
The other mineral commonly observed in mineralization in the study area is goethite. Goethite observed on both XRD and oremicroscopyshowsthepresenceofseveraldifferentstages within the mineralization (Fig. 4a b; Fig. 5c-h). Goethite is ob-servedwithdifferentshadesofgreyunderthefirstNicolandhas typicalyellow,orange,andredinternalreflectionunderthese cond Nicol (Fig. 5d, f, h). In some samples, oolitic textures in goethite are very pronounced (Fig. 5g, h). Though these textures are actually sedimentation textures, similar shapes may form in mineralization developing from solutions and melts in some circumstances. Though the resemblance of these textures to bacteria was discussedatfirst,laterstudiesstatethattheyrepresentahydro-      (RAMDOHR, 1980;GÖYMEN & KOÇ, 2000). Additionally, goethite in the study area contains widely observed colloidal textures (Fig. 5c-f), which are known to be sedimentation markers (SCHWARTZ, 1951). Goethite, which also shows brecciated structures, is another indicator of sedimentary formation (Fig. 4a, b).
The Mo and Co contents in ore samples were 2.90-38.50 ppm (average 21.64 ppm) and 4.20-45.60 ppm (ave. 26.94) in the study area, respectively ( Table 2).
The Ba and As concentrations were 148.40-6315 ppm (avera ge 3687.93 ppm) and 15.20-412.00 ppm (ave. 153.29 ppm) in ore samples in the study area, respectively (Table 2). Samples from the study area had Sr/Ba ratios from 0.07-1.32 (ave. 0.28).
The geochemical data for ore samples from the study area were plotted on a Fe-(Ni+Co+Cu)x10-Mn ternary diagram ( Fig.  6a; BONATTI et al., 1972). Accordingly, all samples were distributedinthehydrothermalfield.

REE Geochemistry
The REE content of samples was used to assess the geochemical parameters of ore mineralization in the study area. REE, commonly used for assessing sources, were analyzed in 20 ore samples taken from the study area. Analysis of the results and some calculations are given in Table 3. ΣREE data had values from 2.70-62.70 ppm with an average (ave.) 28.00 ppm. Additionally, the LREE/HREE ratio in ore samples from the study area was 0.95-9.78 (ave. 5.38) and this value shows that LREE values were enriched compared to HREE values. This enrichment is 0.31-8.82 (ave. 2.55) ratios (Fig. 7). Additionally, Eu and Ce anomalies were assessed. REE data were normalized to chondrite and plotted on spider diagrams (Fig. 7). As seen on the spider diagram for the Eu anomaly, there is a high positive anomaly (Fig. 7). When anomaly values are calculated with the formula Eu*=Eu N / [2/3Sm N +1/3Gd N ], apart from one sample, all displayed a high positive anomaly (0.88-48.10, ave 9.94) (Tablo 3). In some situations, La enrichment causes false-negative Ce anomalies (BAU & DULSKI, 1999;KATO et al., 2006;PLANAVSKY et al., 2010). Forthisreason,theCe*anomalyisdeterminedwithtwodifferent calculations. Ce*=Ce N /[2/3La N +1/3Pr N ] and Pr*=Pr N / (Ce N ×Nd N ) 1/2 calculations were performed. With Ce* calculations, negative anomalies were supported for all samples (0.02-0.88, ave 0.58) (Tablo 3). As a result of Pr* calculation, though 6 samples were observed to have a positive anomaly, 14 samples were observed to have a negative anomaly, and the negative anomaly observed in most samples supports the Ce* calculations (Table 3).

Fluid Inclusion Petrography and Microthermometry
Fluid inclusion studies were performed on four samples taken fromquartzveinswithnearly1cmthicknesslocatedwithincar-bonaterocksintheEğercivillageferromanganesemineralization.Alongtheveins,quartzcrystalsgrowfromthesurfacesof the wall rock towards the centre of the veins, and they have zoned growth structures (Fig. 8a). In this structure, twinned growth zones are found symmetrically on both sides of the veins, and in thefinalstage,quartzcrystalsfillthecavityinthecentreofthese growth zones. Accordingly, zone 1 and zone 2 correspond to the stageIandstageIIquartzformations,respectively,whilethefi-nalstagequartzfillinginthecentreisequivalentto3 rd stage
When the Sr/Ba ratio is examined, if this ratio is larger than 1, the environment is marine; if it is lower than 1, it indicates the presence of continental freshwater in the formation (XIE et al., 2006;XU et al., 2011). This ratio is variable in sedimentary Mn deposits (DOE et al., 2013). In Mn deposits with hydrothermal effects,itis<0.01(DOEetal.,2013).Samplesfromthestudyarea had Sr/Ba ratio values of 0.07-1.32 (ave. 0.28). Apart from two