Identification of Mineral Characterization and Alteration Types in Primary Tin Deposits of Oxide Skarn Type in Batubesi Mining Areas by Petrographic Analysis and Grain Counting Analysis

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PAPER • OPEN ACCESS

Identification of mineral characterization and alteration types in primary tin deposits of oxide skarn type in Batubesi mining areas by

petrographic analysis and grain counting analysis

To cite this article: M A Hendrawan et al 2022 IOP Conf. Ser.: Earth Environ. Sci. 1108 012042

View the article online for updates and enhancements.

Identification of mineral characterization and alteration types in primary tin deposits of oxide skarn type in Batubesi mining areas by petrographic analysis and grain counting analysis

M A Hendrawan¹, J Pitulima^1*, and Guskarnali¹

1Mining Engineering Department, Bangka Belitung University, Balunijuk Village, Merawang District, Bangka Belitung Province, 33712, Indonesia

*Email: [email protected]

Abstract. The presence of primary tin ore on Belitung Island can be found in several areas with varying amounts of presence. One area that has the potential is the Batubesi TB area, Burung Mandi Village, Damar District at East Belitung Regency. This research aims to identify mineral assemblages and alteration types in oxide skarn deposits. The methods used are outcrop observation, sampling, and mineralization-alteration identification. Testing of rock samples through petrographic analysis is to identify minerals through their polarization optical properties and GCA analysis (Grain Counting Analysis) is to determine specific types of minerals that cannot be seen through petrographic analysis. Macroscopically, oxide skarn deposits have a greenish-brick red, black appearance which is dominated by ore minerals (iron oxide, iron carbonate, and iron sulfide), and in some parts chlorite mineral dissemination. Based on the observation result of the optical properties of the rock samples, metallic minerals other than those that have been directly identified were found, such as ilmenite, siderite, cassiterite, and chlorite.

The results of the GCA analysis indicate the presence of cassiterite, pyrite, quartz, siderite, hematite, and limonite minerals. Based on these minerals, it can be seen that the type of alteration in the study area is skarn alteration.

1. Introduction

Belitung Island is one of the many areas in Indonesia that has abundant mineral resource potential. One of them is tin which is a non-renewable mineral. The need for tin is currently widely used in applications for human technology needs. In 2020 the world's use of tin is used for soldering (48%), chemicals (17%), tin plates (12%), batteries (7%), corrosion-resistant metal coatings or alloys (7%) and others.

(9%) [1]. From the many uses of tin metal along with the times, this has an impact on the increasing demand for tin throughout the world.

The increasing demand for tin in the world also increases tin production from exploration companies, exploiting tin around the world. This increase in tin production is certainly supported by increased exploration of new resources and reserves for each tin-producing company, but world tin exploration is still dominated by secondary or placer deposits of around 70% of world tin production [2]. PT Timah is one of them, as the largest tin company in Indonesia and the second largest tin producer in the world, until now, exploration of secondary/placer tin deposits is still dominated. However, along with the times, PT Timah has also started to mobilize by conducting exploration activities for primary tin deposits as evidenced by the existence of a Mining Business License (IUP) since 2015 which is spread over the

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Riau Islands and Bangka Belitung Islands [3]. This activity resulted in primary tin mines which are still producing, such as the Pemali and Paku mines on Bangka Island and Batubesi on Belitung Island.

Batubesi is one of the primary tin deposit producing areas on Belitung Island, this is evidenced by the existence of exploration and exploitation activities in the area. Regionally, the geology in the study area is composed of limestone diorite and the Kelapakampit Formation of Permo Carbon age [1]. The initial research was carried out by Ngadenin et al (2017), but the research was more directed to the study of mineralization of metallic and radioactive elements for the research of the Center for Nuclear Minerals Technology - BATAN. The presence of metal deposit traps in the Batubesi area has generally been identified both based on the type of mineral and the concentration of its presence, but identification of detailed deposit types such as oxide skarn deposits, for example, has not been fully resolved, so identification of mineralization and alteration types in this type of deposit is needed to understand the geological order in the Batubesi area in more detail.

2. Method

This research was conducted by identifying samples of oxide skarn deposits taken directly from the IUP TB Batubesi, Burung Mandi Village, Damar District, East Belitung Regency. Identification of mineralization and type of alteration in the oxide skarn deposits of TB Batubesi begins with petrographic analysis which is carried out by making a thin slice of rock to be observed using a Brunel 75 SP polarizing microscope. Petrographic analysis aims to determine the type of deposit and its mineral composition. The fresh precipitate sample was then made a thin incision and observed with a penetrating light polarization microscope. In addition, a GCA test was also carried out on the concentrate material from the processing of oxide skarn at TB Batubesi with a Stereo Model Olympus microscope to identify the mineral content in detail in the processed products of oxide skarn deposition in TB Batubesi.

3. Discussion

Primary tin deposits in TB Batubesi were found to be present in different forms of deposits. This can be seen from the differences in characteristics such as mineral composition related to the process of mineralization stages, deposit type, and the presence of cassiterite mineral as the main primary tin carrier mineral.

The results of geological mapping show that the study area is composed of granite units and metastone sandstone units [4]. The granite unit is composed of biotite granite and hornblenda granite.

Hornblenda granite is one of the characteristics of type I granitoids so that the content of tin, monazite, and zircon is not much compared to type S granite [5][6]. Macroscopically, oxide skarn deposits have the appearance of greenish brown – brick red, black dominated by ore minerals (iron oxide, iron carbonate, and iron sulphide) and in some parts chlorite mineral dissemination is found (Figure 1).

Figure 1. Macroscopic Appearance of Oxide Skarn Deposits That Have Been Thinly Sliced

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Based on these observations, it appears that the sediment has undergone a further oxidation process which is indicated by the presence of limonite minerals in several areas. These observations determined the presence of metallic minerals of the oxide, sulfide, and supergene enrichment groups. The metal oxide minerals found are hematite and cassiterite. The metal sulfide minerals found are pyrite and siderite. Also found metal minerals from supergene enrichment in the form of limonite minerals.

3.1. Petrographic analysis by microscopic observation of thin slices of oxide skarn deposits

Megastrophic observations cannot identify most of the fine-sized metallic minerals. Metallic minerals that are very fine in size are identified through observations through thin slices of rock samples. Based on the observation of the optical properties of the rock samples, metallic minerals other than those that have been directly identified were found, such as ilmenite, siderite, cassiterite, and chlorite.

Secondary alteration minerals in the wall rock can be identified through microscopic observations which represent this alteration zone (Figure 2). The mineral composition of the constituent minerals is microscopically dominated by ore minerals (80%) with black color, very high relief, isotropic, with a size of 0.05 – 0.1 mm in the form of iron oxide minerals (hematite), carbonate oxides (siderite), and iron sulfide minerals (pyrite) which present in dissemination and fill rock fractures. In addition, this observation shows the presence of chlorite mineral (20%) with a light green-green color with parallel or one-way cleavage with a size of 0.05 – 0.2 mm.

Figure 2. Microscopic Appearance of Oxide Skarn Deposit Under a Polarizing Microscope with 30x Difference, (s: Siderite; p: Pyrite; h: Hematite; k: Chlorite) (a) Cross-linked Nicol, (b) Parallel Nicol.

The mineral chlorite is present as an alteration of the biotite granite. The chloritization process from biotite to chlorite is generally accompanied by the formation of mineralization rich in rutile and cassiterite as in the granite in the western part of Nanling, South China [7] so that the presence of cassiterite in the study area is thought to be related to the chloritization process of biotite.

Based on the identified minerals, the hydrothermal alteration temperature range can be seen with reference to Lawless et al, 1988, modification of Pirajno, 2009. This area experiences skarn alteration at a temperature of 250°C - > 300°C as shown in Table 1.

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Table 1. Temperature Indicator of Alteration Zone of Chlorite Fe Sulphides + Carbonate Fe Oxide [9]

Mineral Temperature (◦C)

100 200 300

Hematite

Chlorite

Pyrite

Siderite

Limonite

Referring to Kwak (1987), this alteration zone is included in the skarn alteration. The naming of the skarn alteration zone is based on the presence of the minerals hematite, siderite, and limonite to characterize high temperature skarn, and chlorite and pyrite to identify skarn to low temperature. This alteration zone has a green appearance. The appearance of the green color in the alteration zone is caused by hydrothermal alteration which changes the compositional content of the rock, such as forming the minerals chlorite, biotite, and epidote. Some of the altered rocks in this zone show a distinctive appearance, namely a repeating pattern of mineral alignment (banded) between metallic minerals (dark in color) and non-metallic minerals such as chlorite (light in color).

3.2. Mineral Composition at the processing output of oxide skarn precipitate by GCA test

The mineral composition analysis is carried out in the Mineral Processing Laboratory. The processing sample will then be homogenized first using a splitter tool 4 (four) times and then sifted using a Sieve Shaker tool with 5 (five) levels of sieve size consisting of sizes 20#, 50#, 75#, 100#, and #-100 (in mesh) to get the grain size distribution of the feed. The sieve results are then calculated the cumulative percentage that passes each sieve number as shown in Table 2.

Table 2. Particle Size Distribution of Oxide Skarn TB Batubesi Sediment Treatment Material

Size Fraction Weight (gram)

Detained (%)

% Cumulative Pass

Mesh µm

#20 0.84 13.8 3.12% 96.88%

#50 0.3 18.4 4.16% 92.72%

#70 0.21 93.6 21.16% 71.56%

#100 0.15 136.2 30.79% 40.76%

#-

100 -0.15 180.3 40.76% 0.00%

Total 442.3 100%

The results of the sieving of feed material at sieve numbers #20 to -100# used in the treatment of TB Batubesi oxide skarn deposits have heterogeneous mineral grain sizes and are classified as materials with fine grain sizes. The feed sample that has been diffracted into 5 grain sizes is then analyzed using a microscope using the Grain Counting Analysis (GCA) method.

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Table 3. Composition of Oxide Skarn TB Batu Besi Processing Materials

No Mineral Original Weight Percent (%) Cumulative

#20 #50 #70 #100 #-100 (%)

1 Cassiterite - 0.43% 1.25% 2.28% 4.12% 8.08%

2 Pyrite 0.96% 0.86% 0.82% 0.65% 0.47% 3.76%

3 Quartz - - 3.84% 5.91% 7.42% 17.17%

4 Siderite - - 0.78% 0.97% - 1.75%

5 Hematite 1.41% 2.14% 13.83% 20.98% 28.75% 67.11%

6 Limonite 0.75% 0.73% 0.64% - - 2.12%

Total (%) 3.12% 4.16% 21.16% 30.79% 40.76% 100%

The results of the Grain Counting Analysis (GCA) method can be identified as the main mineral constituent of the processing material from the source of oxide skarn deposits, namely hematite with a content of 67.11%; quartz with a grade of 17.17%; and cassiterite with a content of 8.08%; pyrite with a grade of 3.76%; limonite with a grade of 2.12; and siderite with a content of 1.75%. Observations using a microscope with the largest size were observed on the grain size of the sieve with filter number

#20, at this grain size found interlocked hematite minerals with quartz minerals (Figure 3), this is the trigger why cassiterite minerals are not identified on optical microscopy on sieves numbered filter #20.

Figure 3. The Appearance of Interlock Minerals in Oxide Skarn Processing Materials TB Batubesi

4. Conclusion

Identification of oxide skarn deposits based on petrographic analysis belongs to the type of skarn alteration. The naming of the skarn alteration zone is based on the presence of the minerals hematite, siderite, and limonite to characterize high temperature skarn, and chlorite and pyrite to identify skarn to low temperature. The mineral composition contained based on the Grain Counting Analysis (GCA) method, the main mineral constituent of material is hematite with a content of 67.11%; quartz with a grade of 17.17%; and cassiterite with a content of 8.08%; pyrite with a grade of 3.76%; limonite with a grade of 2.12; and siderite with a content of 1.75%.

References

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[8] Kwak T A P 1987 W-Sn Skarn Deposits Related Metamorphic Skarn and Intrusi Granitoids (Amsterdam: Elsivier Science Publisher)

[9] Lawless J V, White P J, and Bogie I 1998 Important Hydrotermal Minerals and Their Significance Geothermal and Minerals Services Division Kingston Morrison Ltd 7^th edition

[10] Lindgren W 1931 Mineral Deposit (USA: MC Graw-Hill Book Company) Acknowledgment

We gratefully acknowledge the funding from Universitas Bangka Belitung through the RKAKL Jurusan Teknik Pertambangan Fakultas Teknik for the publication of this paper, and also we would like to thank to all those people who have helped in this research.