The Study of Hydrothermal Alteration and Type Study of Primary Tin Mineralization in Tsk. Pengarem, Southern Bangka Island

Research on hydrothermal alteration mineral and mineralization type of primary tin was conducted in Pengarem village, South Bangka District. This research attempted to find out the type and mineralogy alteration of the site. The methodology involved lithological and structural observation, and X-Ray Diffraction (XRD) analysis. Litho logy constructing the bed was commonly sandstone unit. The developing alteration in this site consisted of argilic zone that characterized by clay minerals such as kaolinite and ilite. Primary tin mineralization developing in this site was polymetallic vein mineralization. The veins developed in sandstone unit, had relatively small size, and spreaded locally. The veins were consisted of quartz unit carrying tin mineralization (cassiterite) and associated with zinc oxide minerals that were ilmenite and hematite. The typical tin mineralization in this site was mineralization in gozzan unit, and was the result of supergene process carried by mineral cassiterite that associated with minerals iron oxide such as ilmenite and goethite.

3. In the typical deposits, point h. metasomatism: "This deposit is formed by precipation process that comes from sodium chloride liquid that is rich with metal elements (syssedimentary) that formed in the edge of the alteredgranitoidafter hydrothermal alteration". This should read: 1. In the Abstract section: "The typical tin mineralization in this site was mineralization in gozzan unit, and was the result of supergene process carried by mineral cassiterite that associated with minerals iron oxide such as ilmenite and goethite" [1].

2.
In type of alteration , point 7: "Muscovitization is hydrothermal alteration process that characterized by the presence of the mica mineral accumulation such as muscovite that associated with minerals that compiling the intrusion body such as biotite, feldspar, and plagioclase" [1]. 3. In the typical deposits, point h. metasomatism: "This deposit is formed by precipation process that comes from sodium chloride liquid that is rich with metal elements (syssedimentary) that formed in the edge of the alteredgranitoidafter hydrothermal alteration" [1].
Thus, I just add one reference that I missed: [1]

Introduction
Tin is one of the Indonesian main export commodities, due to its limited spread, its availability in Indonesia makes this country becomes one of the biggest tin producers in the world. Bangka Island is one of the potential regions that provides abundant source of tin in this country. However, the contribution of this region in 2014 was about 30% of the tin's world.
Tin formation spreading in Bangka Island is formed by tectonic and magmatic processes that producing granitic stones. Also, Indonesia's geographical position that is between Sibumasu, East Malaya and Terrane SW Borneo blocks (figure 1), known as Southeast Asia's tin belt terrain that ends in Bangka and Belitung Islands [1], the important and rich tin producers in the world [2] contributes to the potential source of primary tin deposit.
People utilize tin for industry and daily life support such as solder, metal coating, and metal alloys (with bronze, platting, and conductor). Due to the rampant and continuous secondary tin It actually requires the further research on the uncovered primary tin that has been discovered in Bangka Island, particularly to examine the types of deposit such as lithological characteristic, type of alteration, and type of mineralization of the each deposit. This research would discuss about the alteration and the mineralization of the stone that carrying primary tin. Further informations about alteration types that develop in the research location that containing potential tin would be presented as well.

Alteration
Hydrothermal alteration is the interaction process between hydrothermal fluid and rocks, and this interaction induces mineralogical, chemical, and textural alteration in the rocks as well as the fluid itself [3]. The alteration depends on some factors such as typical rock, composition and chemical concentration of the hydrothermal fluid, pressure and temperature condition of the reaction process [4], alteration process of the hydrothermal and the rocks produces various chemical reactions such as hydrolysis, hydration-dehydration, metasomatism, decarbonation, silification, silication, oxide reduction (redox), carbonatization, desulfidation, sulfidation, hematisation, and fluoridation.

Type of Alteration
The common types of alteration in primary tin deposit are seritisation, chloritisation, turmalinisation, and silicification. But there will be other alterations that might be resulted such as feldspatisation, muscovitization, argilization, and greisenization [5].
The aforementioned alteration types are:

1.
Seritisation is hydrothermal alteration process induced by sericite mineral and quartz. Seritisation process in granite rocks induces feldspar mineral and mica change to become sericite mineral [6].

2.
Chloritisation is hydrothermal alteration process that alter the composition of Fe : Mg in an ore. Chlorite mineral is produced by alteration of mafic minerals in their bearing rocks and is generally occurred along tin veins [6].

3.
Turmalinisation is hydrothermal alteration process associated with deposits that formed in medium-high temperature such as in tin and gold veins. Tourmaline minerals develop well around the rocks and the veins.

4.
Silicification is hydrothermal alteration process that characterized by the increasing amount of quartz mineral or silica in altered rocks. Silicification is often used as indicator of ore deposit [6].

5.
Greisenization is hydrothermal alteration process that characterized by the presence of quartz, muscovite mineral as well as the presence of accessory minerals such as topaz, tourmaline, and fluoride that are formed in granite rocks in the end of magmatism process. Greisenization commonly develops in upper surface of the intrusion contact of the granite and occasionally emerges as stockwork [6]. 6.
Feldspatisation is hydrothermal alteration process that is frequently occurred in metasomatism process of the potassium or sodium minerals. Feldspatisation generally produces potash feldspar or albite minerals [6]. 7.
Muscovitization is hydrothermal alteration process that characterized by the presence of the mica mineral accumulation such as muscovite that associated with minerals that compiling the intrusion body such as biotite, feldspar, and plagioclase. 8.
Argilization is hydrothermal alteration process that characterized by the presence of dickite, kaolinite, piropilit and quartz minerals [6].

Types of Primary Tin Deposit
Smirnov (1977 in (5)) divided primary tin deposit into three categories:

Stanniferous pegmatites
It is typical deposit that associated with the deep granite intrusion, and the presence of pegmatite and casiterite-quartz ore. Pegamatite commonly has the rougher crystal size.

2.
Quartz-cassiterite. These typical deposits are vein, stockwork and greisens that characterized by the bigger crystal size of cassiterite and tungsten and associated with the formation of stanniferous pegmatites.

3.
Sulfide cassiterite This typical deposit formes group of cassiterite that contains the abundant amount of sulfide, iron bearing silica and both of them. While Hosking (1979 in [7]) divided the classification of tin deposit into 13 variations, but merely 11 of them were primary. This deposit is to accommodate tin deposit that contains great amount of sulphide minerals.

Geomorphology
According to geomorphological data analysis, the area study was slowly low eroded hills (hill with low erosion) and relatively flat slope, this formation was induced by peneplanation process or continuous flattening as a result of significant process in Bangka Island, thus it remains some hills and mountains with relatively high elevation and generally are consisted of lithology of igneous rocks.

Stratigraphy
According to Geological map of Southern Bangka sheet with scale 1 : 250.000 [8]

Geological Structure
Geological structure analysis developing in Southern Bangka is very necessary to generate fractures to produce magmatic hydrothermal fluid. Based on Geological map Southern Bangka sheet scale 1 : 250.000 [8] that was published by Geological Research and Development Center Bandung, developing structure in Southern Bangka was join carrying quartz and iron oxide minerals with various directions, flat fault toward northeast-southwest, normal and going up fault toward northwestsoutheast, according to field observation, it was difficult to find the indications of primary geological structure in this location due to erosion process and intensive weathering.

Analysis Methodology
The analysis methodology employed in this study was mineralogy and geochemical analysis. Mineralogy analysis involved petrography and XRD analysis.  Petrography This analysis was conducted for rocks by observing the incision of the rock to observe the composition, texture, structure, relation and the stages of vein formation to identify rock formation process.  X-Ray Diffraction (XRD) Analysis XRD was conducted twice, by bulk analysis or the whole rock composition and clay analysis to determinate clay mineral. Clay analysis emphasized on clay mineral, thus it would reveal the mineral within the clay. The discovered clay mineral would be used to determine typically developing alteration and to find out the temperature as well as pH working on the alteration process.

Geological Control on Mineralization
Geological control involved lithological and structural control that had significant role in forming primary tin mineralization. Some lithology controls were the typical, porosity and permeability of the rock. Structural geology control was the formation of fracture media that enable hydrothermal fluid which carrying mineralization ore to pass even though it was difficult to find big structures due to intensive weathering but veins carrying quartz and oxide became the indications of structural geology control.

 Lithological Control
The lithology that was the host rock in mineralization and was occurred in the field was strong altered rock. It had yellowishbrownish grey color, unidentified its origin rock texture, and commonly had changed to become clay mineral. In another hand, mineralized sandstone in polymetallic vein permeated within ironrock unit where the vein experienced oxidation process while being under surface. In the previous stage, fracturing process of the rock enabled hydrothermal fluid forming quartz vein permeated and contacted host rock. As a result, it enabled mineralization process that producing the association of quartz vein and metal minerals, such as tin ore, and followed by alteration process producing clay minerals.

 Structural Geology Control
Structural geology that developed in Southern Bangka was joins carrying veins, that was not in the same massive vein body, thus it was predicted as debris zone of big faults. While the source rock that was igneous rock that carrying tin mineralization was not found in the field. Primary tin mineralization was found in quartz veins that carrying metal (polymetalic vein). The polymetalic vein develops in sandstone unit but this typical stone was not found in Southern Bangka. Primary tin mineralization in quartz vein carried abundant metals (polymetalic vein). This vein developed in sandstone but not all of the sandstone in Southern Bangka experienced mineralization because the polymetallic vein did not have the similar dispersion as sandstone unit did. There was enrichment of clay minerals in some locations, the clay mineral group consisted of kaolinite and ilite (figure 3).
Geological structure developing in Southern Bangka based on observation and join as well as vein measurement was predicted that the tin mineralization had NNW-SSE direction and was located in argilic alteration zone. It could be interpreted that ore sedimentation in the polymetalic vien had tiny size and spread unevenly (local) within sandstone with gangue mineral such as quartz, and ironoxide (hematite and tin).

Model of Primary Tin Deposit Mineralization
Type of primary tin mineralization developing in Pengarem site closely related to hydrothermal and supergene system. Smirnov (1977, in [2]), mentioned this typical deposit as quartz-cassiterite deposit or deposit with quartz and stockwork vein. This primary tin deposit subsequently was grouped in stanniferous veins type (Hosking, 1979, in [5]), or tin deposit that located within quartz vein, characterized with the presence of the group of metal minerals such as pyrite, magnetite and clay minerals that controlled by structural geology of igneous rock intrusion toward sedimentary rock. Quartz vein carrying tin mineralization in the research location was located in sandstone unit that experienced argilic alteration, composed of quartz, cassiterite, pyrite, and ironoxide (ilminite and gheotite). Besides located in quartz vein, this particular deposit was also located within ironoxide or gozzan that formed by oxidation process of the polymetalic vein. Thus it enabled iron sulfide minerals (pyrite formed iron oxide mineral (geothite and ilminite) (figure 4 and 5).

Conclusions
The formation of primary tin mineralization type gozzan was a result of oxidation process within polymetalic vein. It was characterized by the presence of cassiterite that associated with iron oxide mineral (hematite and goethite). Typical primary tin mineralization in the research location was stanniferous vein, that was quartz vein carrying tin mineral (cassiterite, stanite) or called polymetalic vein. Primary tin deposit in the site was controlled by geological structure with NNW-SSE direction marked by the presence of polymetallic vein within sandstone unit. While mineralization in ironrock or gozzan was occurred as a result of oxidation process within polymetalic process.