![ALTERATION In The GABON FORMATION [PDF]](https://pdfs.asia/img/200x200/alteration-in-the-gabon-formation.jpg)
4 0 8 MB
ALTERATION IN THE GABON FORMATION Ayah Sub District Kebumen District & Cilacap District Middle Java Province Indonesia Isen Renaldo* & Yan Rizal** *) Geological Department Of Sekolah Tinggi Teknologi Mineral Indonesia **) Geological Department Of Institut Teknologi Bandung [email protected] ABSTRACT
INTRODUCTION
Geographycally, the research area is located at 109°23’30’’EL - 109°25’30’’EL & -07°42’00’’SL -07°44’30’’SL with an area of 5x5km research area. Broadly speaking, the research area is located in the southwestern part of central java province.
Alteration is a complex process, which involves changes in mineralogy, chemistry, and rock texture due to interactions between hydrothermal fluids and the rock they pass through (Pirajno, 1992).
Regionally, in the research area there are 2 formations namely the gabon formation (late oligocene) & kalipucang formation (middle miocene). There are 6 rocks unit namely lava, breccia, tuff, intrusion, limestone, and alluvial. There are 3 geological structures in the research area, namely Argopeni flat fault, Kalibangkang flat fault, and Ayah flat fault. This research was conducted to find out the presence of alteration and mineralization in the gabon formation which is intruded by 3 andesite intrusions. This research was conducted using 3 methods, namely megascopic, microscopic, and geochemical (XRD). Analysis of hydrothermal alteration in the study area, divided into 2 alteration zones namely the argilic zone (kaolinite-montmorillonite-pyrite-carbonatequartz) & propilitic zone (chlorite-epidote-pyritecarbonate-quartz). There is a mineralization in the argilic zone with a set of metallic minerals such as azurite-malachite-bornite-pyrite-chalcopyrite-galena. On the mineralized area there are silisified vein with 16,3cm wide. The type of mineral deposit present in the study area is epithermal with low sulfidation type.
Keywords : alteration, mineralization, gabon formation, kebumen.
Hydrothermal fluids is a high temperature volatile liquid (around 100-500°C) in the form of residual cooling magma which is capable of changing and forming certain minerals. In general, the liquid left over from crystallization of magma is siliceous in nature which is rich in alumine and alkaline composition, also containing water and volatile elements (Bateman, 1981). Hydrothermal solutions are formed in the final phase of the magma crystallization cycle and generally accumulate in lithologies with high permeability and weak zones. The interaction between the hydrothermal fluid and the wall rock will cause the conversion of primary minerals into secondary minerals (alteration minerals). Factors that influence the alteration process, depend on the wall rock characteristics, fluids properties (Ph), pressure & temperature condition at the time of the reaction, and the duration of the hydrothermal activity (Corbett & Leach, 1998). Based on the above theory, it can be concluded that the alteration process in the study area occurs due to the interactions between magmatic fluids and soil water. The 3 andesite intrusions in the research area experiences heating (prograde) while it is still in the form of liquid volatile so that its composition changes into hydrothermal fluids. This hydrothermal fluids is estimated able to enter through the crack from the joints caused by the Argopeni fault and Kalibangkang fault, so the lithologies in Gabon Formation (Lava, Breccia, Tuff) experiencing changes. The alteration process, is estimated occurs during early miocene.
1
RESEARCH METHODS The methods that are used to investigate the minerals composition in the argilic zone, is megascopic and geochemical (XRD) since the naming of the clay minerals group can only be research with XRD (X-Ray Diffraction). The methods that are used to investigate the minerals composition in the propilitic zone and mineralization zone is megascopic and microscopic thin section with the zoom scale of 4x from 0,03cm sample incision thickness.
DISCUSSION There are 2 alteration zonation in the research area, which is argilic zone with the mineral assemblage of (Kaolinite-Montmorillonite-Pyrite-CarbonateQuartz) and propilitic zone with the assosiation mineral of (Chlorite-Epidote-Pyrite-CarbonateQuartz). This alteration zonation is determined based on (Guilbert & Park, 1986) which can be seen in the following table :
REGIONAL ALTERATION Based on the previous researcher, there are 2 alteration zone in the research area. According to (Maskuri, 2003) there are argilic zone (quartzchalcopyrite-pyrite-adularia-sericite) and propilitic zone (chlorite-epidote-carbonate). The following is an stage overview of the alteration zoning table according to (Maskuri, 2003) in Gabon Formation :
Table 1.1 Alteration zoning from previous reseacher
Table 1.2 Minerals determination in every alteration zonation After recognizing the minerals assemblage in every alteration zonation, the author divided the research area into 2 zonation alteration which is argilic zone and propilitic zone. The first step taken on this research is to make the map of alteration tracking, with the purpose to find out the direction of the distribution alteration zone based on the minerals assemblage in the research area. The following is the map of alteration tracking according from the data that has been taken in the field : GEOLOGY ENGINEERING FACULTY SEKOLAH TINGGI TEKNOLOGI MINERAL INDONESIA 2023
ALTERATION TRACKING MAP Ayah Sub District Cilacap District & Kebumen District Middle Java Province Indonesia Scale = 1 : 10.000 0
250
500
1.000
Legend : Propilitic Zone (Chlorite - Epidote - Pyrite Carbonate - Quartz) Argilic Zone (Kaolinite - Montmorillonite - Pyrite Carbonate - Quartz) Andesite Intrusion
Information : Ocean
Small River Big River
Minor Contour with 25 Meters Interval
Tracking
Mayor Contour with 100 Meters Interval
Index Map : Middle Java Province Administration Map with scale of 1 : 1.344.000
RBI Page Rowokole Map with scale of 1 : 25.000
Created By : I.Renaldo (1017009)
Research Area
Faculty : Geology Engineering
Picture 1.1 Alteration tracking map 2
After making of the alteration tracking map, the authors interpret the withdrawal of the alteration zonation based on the alteration tracking map and the minerals assemblage contained in the argilic zone and propilitic zone. The following is the Alteration Map in the research area : A’ GEOLOGI ENGINEERING SEKOLAH TINGGI TEKNOLOGI MINERAL INDONESIA 2023
ALTERATION MAP Ayah Sub District Cilacap District & Kebumen District Middle Java Province Indonesia Scale = 1 : 10.000 0
250
500
1.000
Legend : Color
Mineral Assemblage
Alteration Zonation
Alteration Stage
Alteration Intensity
Altered Lithology
2
Weak Moderate
- Lava Unit - Breccia Unit - Tuff Unit
1
Moderate Strong
- Lava Unit - Breccia Unit - Tuff Unit
- Chlorite - Epidote Propilitic - Pyrite - Carbonate - Quartz - Kaolinite - Montmorillonite - Pyrite - Carbonate - Quartz
Argilic
Andesite Intrusion Non Altered
Information : Minor Contour with Interval of 25 Meters
Big River
Mayor Contour with Interval of 100 Meters
Small River A’
Ocean
A
Cross Section Andesite Quarry
Transform Fault
Limestone Quarry
Fault Prediction
Ore Minerals Quarry
Index Map : Middle Java Province Administration Map with scale of 1 : 1.344.000
RBI Page Rowokole Map with scale of 1 : 25.000
Research Area
A A N11 E
N191 E A’
Penampang Alterasi Skala = 1 : 10.000 H:V=1:1
500m 400m 300m
Ayah Fault
500m 400m 300m
Argopeni Fault X
200m
200m
X
100m 0m
?
?
100m 0m
?
Created By : I.Renaldo (1017009)
Faculty : Geology Engineering
Picture 1.2 Alteration Map As we can see on the alteration map, that the alteration distribution are following the spreading direction of the Argopeni fault and Kalibangkang fault which is southwest - northeast. This is because there are joints that are created around the Argopeni fault and Kalibangkang fault so the hydrothermal fluids are entering through this joint, changing the primary minerals from the wall rock in the Gabon Formation which is Lava unit, Breccia Unit, and Tuff unit into alteration / secondary minerals. There are 3 intrusions with andesitic type (marked with red color in alteration map) which is predicted is the causes of alteration in the research area. Alteration in the research area can be formed because there are metasomatism process between 3 andesite intrusions and the wall rock in Gabon Formation. Metasomatism is a changing process of a physical and chemical composition of a rock that are occured because there are interaction between wall rock and hydrothermal fluid. According from the dipping dicection of the cross section, argilic zone are formed first.
ARGILIC ZONE This alteration zone is marked with pink color in the alteration map and has an area of around 20% total of the research area. The minerals assemblage that are founded in this zone are kaolinite-montmorillonitepyrite-carbonate-quartz. Based on the megascopic observation, the alteration intensity of this zone is generally moderate-strong which changes the primary minerals composition of the lava units, breccia units, and tuff units from Gabon Formation. The following is an overview of the argilic zone in the research area : B
A
E
W
A’
C
D
Chalcopyrite
Galena
Clay Minerals
Pyrite
3
Picture 1.3 Argilic zone on the lava unit (A) Distant scale photo (B) Close-up scale photo (C) Observation point in the alteration map marked with black circle (D) Sample picture. B
A
S
Silisified Vein
N
Picture 1.6 XRD analysis on the argilic zone in the tuff unit from the Gabon Formation. After recognizing the mineral composition in the argilic zone based on megascopic & geochemical (XRD) analysis, the authors conducted an analysis to determine the alteration stability temperature based on the mineral assemblage. This analysis was determined using the classification of (Lawless ,etc. 1998) which the argilic zone has a stability temperature from 120-200°C. The following is the table of temperature stability in the argilic zone :
A’
D
C
Pyrite
Temperature Stability ( C)
E Kaolinite
Pyrite Clay Minerals
Calcite Galena
Picture 1.4 Argilic zone on the breccia unit (A) Distant scale photo (B) Close-up scale photo (C) Observation point in the alteration map marked with black circle (D) Breccia sample picture (E) Silisified vein sample picture. A
B
S
N
Crustiform
A’
C
E
D
Galena
Montmorillonite
Pyrite Calcite Quartz
Table 1.3 Temperature stability in the argilic zone PROPILITIC ZONE This alteration zone is marked in green color on the alteration map and has an area of around 40% total of the research area. The minerals assemblage that founded in this zone are Chlorite-Epidote-PyriteQuartz-Carbonate. Based on the megascopic observation, the alteration intensity of this zone is generally weak-moderate which changes the primary minerals of the lava units, breccia units & tuff units from Gabon Formation. The following is an overview of the propilitic zone in the lava unit : A
B
Infilling
Quartz
Clay Minerals
Pyrite
Picture 1.5 Argilic zone on the tuff unit (A) Distant scale photo (B) Close-up scale photo (C)Observation point in the alteration map marked with black circle (D) Infilling close-up scale photo (E) Sample picture The following is the XRD analysis from argilic zone on the tuff unit from Gabon Formation which contain a clay mineral of Kaolinite & Montmorillonite :
Chlorite
C
D
Stockwork
E
Picture 1.6 Propilitic zone on lava unit (A) Distant scale photo (B) Close-up scale photo (C)Observati on point in the alteration map marked with black circle (D) Stockwork texture (E) Sample picture. As we can see that there is a chlorite prensence on megascopic description, which chlorite is the key mineral from the propilitic zone (Guilbert & Park, 1996). In order to have a more accurate result, the authors doing a microscopic analysis with 4x zoom scale. The following is the microscopic analysis from propilitic zone on the lava unit from the Gabon Formation : 4
authors perform a microscopic analysis with 4x zoom scale. The following is the microscopic analysis from propilitic zone on the breccia unit from the Gabon Formation :
Picture 1.7 Microscopic analysis from lava unit on the propilitic zone. Next lithology unit in the Gabon Formation is an altered breccia unit on the propilitic zone. The following is the field picture of the breccia unit on the propilitic zone in the Gabon Formation : B
A
Picture 1.9 Microscopic analysis from breccia unit on the propilitic zone Next lithology unit in the Gabon Formation is an altered tuff unit on the propilitic zone. The following is the field picture of the tuff unit on the propilitic zone in the Gabon Formation :
A
B
W
E
S
N A’
C
D A’
C Chlorite
Picture 1.8 Propilitic zone on breccia unit (A) Distant scale photo (B) Close-up scale photo (C) Observation point in the alteration map marked with black circle (D) Sample picture. As we can see that there is a chlorite prensence on megascopic description, which chlorite is the key mineral from the propilitic zone (Guilbert & Park, 1996). In order to have a more accurate result, the
D
Oxydation
Pyrite
Picture 1.10 Propilitic zone on tuff unit (A) Distant scale photo (B) Close-up scale photo (C) Observation point in the alteration map marked with black circle (D) Sample picture. In order to have a more accurate result, the authors perform a microscopic analysis with 4x zoom scale The following is the microscopic analysis from the 5
propilitic zone on tuff unit from the Gabon Formation : 2
1
Information :
1
= First Alteration Stage
2
= Second Alteration Stage
Table 1.5 Alteration stages Picture 1.11 Microscopic analysis from tuff unit on the propilitic zone. After recognizing the mineral composition in the propilitic zone based on megascopic & microscopic, the authors conducted an analysis to determine the alteration stability temperature based on the mineral assemblage. This analysis was determined using the classification of (Lawless., etc. 1998) which the propilitic zone has a stability temperature from 240320°C. The following is the analysis table of temperature stability in the propilitic zone : Temperature Stability ( C) Chlorite Epidote Pyrite Calcite Quartz
Table 1.4 Temperature stability in the propilitic zone ALTERATION STAGES Alteration stage intend to determine which alteration zonation were formed first in the research area, and which alteration zonation were formed later. This interpretation also includes an analysis to determine the pH of each alteration zones. This analysis was interpreted based on (Corbett & Leach, 1998) classification. The following is an overview of the alteration stages on research area :
As we can see that the argilic zone were formed first with mineral aggregate of kaolinite (K) smectite (Sm) -quartz (Ku) and propilitic were formed later with mineral aggregate of chlorite (Kl) - silica - carbonate (Kb). Ph number on the argilic zone is 5 and Ph number on the propilitic zone is 7. This means that there are a changes of temperature & pH from the hydrothermal fluid when the metasomatism process were occured on the research area.
ORE ESTIMATION After recognizing the temperature stability data & pH stability data on every alteration zonation, the authors interpreted an ore elements estimation that will be founded on the research area. This interpretation are determined based on solubility diagram. This solubility diagram can be determined with the provision of temperature data & Ph data on every alteration zonation in the research area. But this estimation is still predicted, to have a more accurate result, a drilling data and laboratory study are needed due to the lack of data. This estimation are interpreted based on (Corbett & Leach, 1998) classification. The following is an overview of the solubity diagram to estimate the ore element that will be found on the research area : 6
MINERALIZATION
Information :
= Argilic
= Propilitic
= PH combined between argilic & propilitic
Picture 1.12 Solubility diagram As we can see from the diagram above, that the estimation of ore elements in the research area are Au (Gold), Cu (Copper) & Zn (Zinc). ALTERATION TEXTURE Texture is the appearance of a rock related to the size, shape and arrangement of minerals / grains in the rocks. Alteration texture is an appearance of a secondary minerals that are founded in the altered rocks. There are several of alteration texture that are founded in the altered lava unit, altered breccia unit and altered tuff unit from the Gabon Formation. This indicated that the alteration intensity in the Gabon Formation are relatively strong. The following are the variety of alteration texture that are founded in the research area : Location
Texture Name
Mineralization is a process that describes the set of a new mineral called secondary minerals and ore minerals in a rock composition, which has a quite of sale value caused by hydrothermal process. There are several factors that mineralization can be occured, which is : - Prensence of hydrothermal fluid as a carrier - Joint as a pathways for minerals deposition - Available free spaces of joint / crack for the infilling process - Presence of a hydrothermal fluids consentration are high enough to build ore minerals - Presence of vein - Enough temperature, pressure and pH - Enough time when the mineralization process is begin There are a mineralization that are occured in the argilic zone from the Gabon Formation which is containing a set of metallic mineral assemblage of (azurite-malachite-bornite-galena-chalcopyritepyrite). The following is the field overview of the mineralization that are occured in one of the quarry from the argilic zone : A
Texture Picture
W ST-19
Infilling
ST-37
Vug & Cavity Filling
B
C
E
Bornite
D Chalcopyrite
Pyrite
ST-87
ST-41
ST-19
Disseminated & Replacement
Stockwork
Crustiform
Table 1.6 Alteration texture
Malachite
Azurite
Picture 1.13 Mineralization (A) Distant scale photo (B) Close-up scale photo (C) Observation point in the alteration map marked with black circle (D) Sample picture. As we can see that from the megascopic there are a presence of several ore minerals which is bornitechalcopyrite-pyrite-azurite-malachite-galena. To obtain a more accurate result, a microscopic analysis was performed on the mineralization from argilic zone. The following are the picture of a microscopic analysis from mineralization sample in one of the quarry that are located in the argilic zone : 7
MINERAL DEPOSIT The type of mineral deposit is quite important for the interpretation of the presence of ore minerals. The type of mineral deposit can be determined based on certain factors, namely the type of intrusion, the type of host rock, the type of alteration zones, the composition of the altered minerals, the composition of the metal comodity, and the type of alteration texture. Determination of the mineral deposit was interpreted based on (Hedenquist., et al. 2008). Based on the analysis that has been done, the type of mineral deposit on the research area is an epithermal deposit with low sulfidation (LS) type. The following is the table types of mineral deposit in the research area :
Picture 1.14 Microscopic analysis from quarry in the mineralization on argilic zone.
HYDROTHERMAL DEPOSIT TYPE Magmatic BasalticIntrusion UltraBasaltic BasalticHost Rock UltraBasaltic Alteration Zonation
Greisen Granitic Granitic
Greisen
Porphyry
Skarn
Epithermal (H.S)
Epithermal (L.S)
GraniticAndesitic GraniticAndesitic
GraniticAndesitic
Andesitic
Andesitic
Carbonate
Volcanic, Sedimentary
Potassic Skarn Propilitic
Advanced Argilic Propilitic Argilic
Volcanic, Sedimentary Phyllic, Argilic, Propilitic, Advanced Argilic
Garnet, Diopside Magnetite Wolasonite Tremolite Biotite, Chlorite
Kaolinite Alunite Crystoballite Diaspore Illite
Sericite, Illite Chlorite, Epidote Calcite, Kaolinite
Barite Gypsum Anhidrite Illite Quartz
Potassic,Phyllic, Argilic,Propilitic, Advanced Argilic
Biotite, K-Feldspar, Topaz Quartz, Sericite, Quartz Pyrite, Illite, Muscovite Epidote, Chlorite Calcite, Tourmaline Kaolinite Alunite
Alteration Minerals
Volcanic Massive Sulfide (VMS)
DasiticGranitic VolcanicDasitic Silisification Argilic
Ore Minerals
Chromite Pendlandit Magnetite
Calciterite Wolframite Scheelite
Bornite Chalcocite Chalcopyrite Molibdenit
Bornite Chalcocite Chalcopyrite Molibdenit
Enargite Luzonite Tenantite
Sphalerite Galena Chalcopyrite
Sphalerite Galena Chalcopyrite
Metal Comodity
Cr, Ni, Pt
Sn, W
Cu, Au, Mo, Sn, W
Cu, Au, Mo, Sn, W
Au, Cu, Ag
Au, Ag
Zn, Pb, Cu, Au, As
Disseminated Disseminated Disseminated Stockwork Stockwork Vein
Disseminated Stockwork Vein
Massive Disseminated Replacement
Vein Stockwork Disseminated
Massive Bedding
Relatively High Consentration on the alteration zone with high tonnage and low rate
Relatively High Consentration on the alteration zone with high tonnage and low rate
Equivalent with active Volcanic system
Equivalent with active Volcanic system
Assosiated with underwater volcanic activity
Texture
Other
Direct crystalization from magma
Information :
= Hydrothermal Deposit Type in the research area
Red Font = Characteristic founded in the research area
Table 1.7 Mineral deposit type 8
SUMMARY There are 2 alteration zonation in the research area which is argilic zone (kaolinite-montmorillonitepyrite-carbonate-quartz) and propilitic zone (chlorite -epidote-pyrite-carbonate-quartz). There are mineralization that are occured in the argilic zone with metallic mineral set of (bornite-azurite-pyritemalachite-galena-chalcopyrite) with mineral deposit type of epithermal (low sulfidation).
REFERENCES - Bateman. A.M. dan Jensen. M.L. 1981: Economics Mineral Deposits. John Wiley &son, Inc. New York. - Corbett, G. J., dan Leach, T. M.,1998: Southwest Pacific Rim gold-copper systems : structure, alteration, and mineralization. Society of Economic Geologist Special Publications Number 6. USA : Society of Economic Geologist, p. 243. Townsville. - Guilbert, J.M., dan Park, C.F. 1986: The Geology of Ore Deposits. W.H. Freeman and Company. New York - Lawless, J.V., White, P.J., Bogie, I., Paterson, L.A., and Cartwright, A.J. 1998: Hydrothermal Models, Mineral Deposits In The Arc Setting : Exploration Based On Mineralization Service. Kingston Morrison Mineral. Auckland. - Maskuri, F. 2003: Studi Alterasi Hidrotermal Daerah Karangbolong, Kabupaten Kebumen, Jawa Tengah. Faculty of Teknologi Mineral UPN “ Ve t e r a n ” Yo g y a k a r t a . Yo g y a k a r t a . - Pirajno, F. 1992: Hydrothermal Mineral Deposit. Cambridge University. Cambridge. Prayogo, T., Tresnadi. H., Zikri. S., Nugroho. R. 2021: Tinjauan Geologi Deposit Bijih Pada Daerah Kalirejo, Kulon Progo. Pusat Teknologi Pengembangan Sumberdaya M i n e r a l ( P T P S M ) . Ta n g e r a n g S e l a t a n . - Sibarani. 2008: Mineralisasi Endapan Epitermal dan Sistem Wrench Fault. Universitas Sriwijaya. Palembang. - Wardhany. F., Isyqi, Puswanto. E., Ansori, C.2019: Alterasi Hidrotermal di Daerah Tinggian Karangbolong, Kebumen, Jawa Tengah. Lembaga Ilmu Pengetahuan Indonesia (LIPI). Kebumen.
9
