KURVATEK Vol.
No.
April 2024, pp.
e-ISSN: 2477-7870 p-ISSN: 2528-2670
ALTERATION AND MINERALIZATION STUDIES IN
THE JEBLOGAN AREA.
KARANGTENGAH.
WONOGIRI,
CENTRAL JAVA
Awang Subang Negara1* Department of Geological Engineering.
Universitas Pembangunan Nasional AuVeteranAy Yogyakarta Jalan Ring Road Utara.
Condongcatur.
Depok.
Sleman.
Yogyakarta 55283.
Indonesia *Email corresponding: awangsn94@gmail.
How to cite: A.
Negara, "Alteration and mineralization studies in the Jeblogan area.
Karangtengah.
Wonogiri.
Central Java," Kurvatek, vol.
9, no.
1, pp.
73-82, 2024.
doi: 10.
33579/krvtk.
[Onlin.
Abstract Ai The research area is located in Jeblogan.
Karangtengah.
Wonogiri.
Central Java.
This study aims to investigate the hydrothermal alteration and mineralization.
Geological structures present in the research area include faults and fractures.
These faults are well-developed trending NE-SW.
NW-SE, and N-S as pathways for fluid ascent to the surface, thereby influencing alteration patterns.
Mineral alteration assemblages in the research area, based on petrographic, mineragraphy, and XRD analysis, result from hydrothermal processes and include mineral assemblage zones such as Quartz A Silica A Pyrite.
Alunite Pyrophyllite A Zunyite A Quartz A Hematite.
Illite Halloysite A Smectite A Kaolinite A Quartz, and Chlorite Calcite Epidote A Pyrite.
Mineralization found in the research area includes Chalcopyrite.
Sphalerite.
Pyrite.
Chalcocite, and Galena.
Based on the characteristic parameters of the deposit type and laboratory analysis, the deposit type at the research location is low-sulfidation epithermal deposit and intermediate-sulfidation deposit.
Keywords: Hydrothermal Alteration.
Karangtengah.
Mineralization.
Wonogiri.
INTRODUCTION
The southeastern part of Wonogiri Regency is predominantly composed of Tertiary volcanic rocks, classified into Mandalika Formation.
Arjosari Formation, and Semilir Formation .
Typically, primary minerals formed from volcanic origins are associated with rocks that have undergone hydrothermal alteration, intrusions within the central volcanic facies, and are associated with subvolcanic intrusions .
Tectonic activity in the area has evolved three times during the Early Miocene.
Middle Miocene, and Pliocene-Pleistocene periods .
One of the potential hydrothermal deposits can be found in Karangtengah Subdistrict.
Wonogiri Regency.
The presence of indications of mineral deposits possibly due to intrusive rocks penetrating volcanic rocks and well-developed geological structures in the study area has the potential for hydrothermal alteration and valuable ore mineralization.
This background motivated the author to conduct research in this area.
II.
METHODS
The goal of study is to investigate hydrothermal alteration and mineralization.
It involves utilizing existing data and conducting field observations such as lithology identification and structural geology measurments, followed by rock sampling for laboratory analyses such as Petrography.
Mineragraphy, and XRD.
The results of field observation delineates lithostratigraphic units, identifies geological structures like fractures and faults with the results in the form of a geological map.
The geological map are use as the basis for making alteratin map, characterizes alteration zones based on petrographic and XRD analyses.
Mineralization findings including valuable ore minerals, and determines the deposit type through characteristic data assessment.
The conclusion is to determine the deposit type based on several researchers.
This explanation is outlined in the flow chart below (Fig.
Received December 11, 2023.
Revised April 8, 2024.
Accepted April 16, 2024 DOI : https://doi.
org/10.
33579/krvtk.
Figure 1.
Flowchart of the study i.
RESULTS AND DISCUSSION
Stratigraphy The stratigraphic classification in the study area uses the naming of lithostratigraphic units with an unofficial naming system .
, which names rock units based on observable physical lithological characteristics in the field, considering lithological type and uniformity and the stratigraphic position relative to underlying and overlying units.
Arjosari breccia-tuff Unit This unit occupies an area of 65%, spreading to the south and northwest of the research area.
This unit has undergone alteration almost entirely.
Field appearances of this rock unit include intercalations of Tuff Breccia.
Polymictic Breccia.
Tuff, with interbeds of Lava.
Conglomerate.
Shale.
Sandy Marl, and Marl Limestone with intercalations of volcanic breccia and limestone breccia.
Dominantly, the lithology of this rock unit has been significantly altered.
Arjosari breccia-tuff Unit is the oldest unit in the study area and has a stratigraphic relationship of interfingering with Mandalika lava-andesite Unit.
The contact between the tuff breccia and lava is observed in the field.
The stratigraphic relationship with Mandalika lava-andesite Unit is shown by the morphology, where the lava is positioned at a higher topographic level than the Arjosari breccia-tuff Unit.
Mandalika lava-andesite Unit Mandalika lava-andesite Unit in the study area covers 13% of the area, mainly located in the northern part of the research area.
This unit has undergone significant alteration and is associated with thrust fault The lithological characteristics of Mandalika lava-andesite Unit consist of andesitic lava with altered breccia interspersed throughout the study area.
Stratigraphic relationships in Mandalika lava-andesite Unit are demonstrated by the higher topography of the lava compared to Arjosari breccia-tuff Unit.
Geological profiles and cross-sections parallel to the strike indicate interfingering relationships between Arjosari breccia-tuff Unit.
Meanwhile, with the Dacite Lithodeme and Andesite Lithodeme, it shows cross-cutting relationships.
KURVATEK Vol.
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e-ISSN: 2477-7870 p-ISSN: 2528-2670 Rohtawu lava-andesite Unit Rohtawu lava-andesite Unit in the study area covers 12% of the area, located in the northeastern part of the research area.
This unit has undergone significant alteration and is associated with lava dome landforms, which are elevated due to resistant rocks.
The lithological characteristics of Rohtawu lava-andesite Unit consist of andesitic lava with well-developed joint and foliation structures that have been moderately altered .
ee Fig.
Figure 2.
Geological Map of the Research Area.
Rohtawu lava-andesite Unit flow is a lateral eruption from the ancient Karangtengah volcano, cutting through Arjosari breccia-tuff Unit and Mandalika lava-andesite Unit before overlying them and intruding into Dacite Lithodeme and Andesite Lithodeme with cross-cutting relationships.
Dacite Lithodeme Dacite lithodeme in the study area covers 6% of the area, located in the central-northern part of the research area.
This unit has undergone significant alteration and is associated with lava dome landforms.
The lithological characteristics of Dacite lithodeme consist of dacitic lava with well-developed joint and foliation structures that have been moderately altered.
In the stratigraphic relationship.
Dacite Lithodeme intrudes into Arjosari breccia-tuff Unit.
Mandalika lava-andesite Unit, and Rohtawu lava-andesite Unit with cross-cutting relationships.
Additionally, it is overlain by the Andesite Lithodeme, showing the topographic characteristics of Dacite Lithodeme being lower than Andesite Lithodeme.
Andesite Lithodeme Andesite lithodeme in the study area covers 4% of the area, located in the northern part of the research This unit has undergone significant alteration and is associated with lava dome landforms.
The lithological characteristics of Andesite Lithodeme consist of andesitic lava with well-developed joint and foliation structures that have been moderately altered.
Stratigraphic relationships of Andesite lithodeme indicate intrusions into Dacite lithodeme and Rohtawu Lava-Andesite unit with cross-cutting relationships.
Alluvial Deposit Unit The alluvial deposit unit covers an area of approximately 1% and is distributed along the rivers in the research area.
In the field, this rock unit consists of loose material and alluvial deposits ranging from clay to boulders resulting from the breakdown of pre-existing rocks in the vicinity that have unconsolidated and Alteration and Mineralization Studies in the Jeblogan area.
Karangtengah (Awang Subang Negar.
DOI : https://doi.
org/10.
33579/krvtk.
have been transported due to fluvial processes.
The stratigraphic relationship of the alluvial deposit unit with the unit below it .
lder uni.
is not in sync.
Geological Structure Fractures Alteration and weathering processes that have occurred extensively in the research area make it difficult to observe tectonic fractures in the field.
Tectonic fractures with ideal conditions for data collection are typically found in lava and breccia units within the Mandalika andesite-lava Unit.
Faults Alteration and weathering processes that have occurred extensively in the research area make it difficult to observe tectonic fractures in the field.
Tectonic fractures with ideal conditions for data collection are typically found in lava and breccia units within the Mandalika andesite-lava Unit Based on stereographic analysis, the rock units in the research area are intersected by left strike-slip faults, right strike-slip faults, and normal faults.
The right strike-slip faults with a southeast to northwest orientation are controlled by the stress patterns from the Middle Miocene Era, while the left strike-slip faults with a southwest to northeast orientation are controlled by stress patterns from the Pliocene Ae Pleistocene Era.
Among the two structural patterns in the research area, the structural pattern resulting from the stress in the Middle Miocene era plays a role in the alteration and mineralization events in the research area.
This is evidenced by the presence of vein mineralization and alteration patterns that follow the geological structural patterns produced by the ancient stress during that era, which is southeast to northwest.
Alteration The presence of dacite intrusion and andesite intrusion is believed to have influenced the alteration of rocks in the research area.
However, not all intrusion and hydrothermal alteration processes result in valuable ore mineral deposits.
The latest intrusion, which is the andesite intrusion, has led to hydrothermal alteration and mineralization.
This is based on the development of geological structural patterns associated with the rise of this intrusion, which contains valuable ore minerals, as well as alteration and mineralization occurring in two previous intrusion bodies.
Quartz Silica A Pyrite (Silici.
This type of alteration is characterized by the abundance of silica minerals (SiO.
such as quartz.
In the research area, this alteration is prevalent in the southwestern, northwestern, and southeastern parts, covering approximately 20% of the total research area.
This type of alteration is often associated with rocks in contact with intrusions, geological structure lines .
aults and fracture.
, or around mineralization vein zones.
In this alteration, the original rock texture of andesite lava and dacite intrusion is almost entirely transformed .
0% secondary mineral.
, with the original texture of the parent rock no longer visible .
ee Fig.
Figure 3.
Appearance of Quartz and Pyrite Minerals Alunite Pyrophyllite A Quartz A Zunyite A Kaolinite A Hematite (Advanced Argilli.
Advanced argillic alteration in the research area is found in small areas in the northwest, southwest, northeast, and central parts of the eastern section, covering 10% of the total alteration area.
Advanced argillic alteration occurs in dacite, tuff, and andesite lava rocks and is characterized by the presence of KURVATEK Vol.
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e-ISSN: 2477-7870 p-ISSN: 2528-2670 minerals such as pyrophyllite, alunite, quartz, zunyite, and kaolinite.
The presence of minerals like pyrophyllite and zunyite (Figs.
4 and .
is a key indicator that the hydrothermal fluids were acidic and hightemperature .
, .
Figure 4.
Appearance of Quartz.
Clay and Alunite Minerals Figure 5.
XRD analysis shows Quartz.
Zunyite, and Hematite Illite Halloysite A Smectite A Kaolinite A Quartz (Argilli.
Argillic alteration in the research area covers a wide area, approximately 45%, and transforms the rock units in the research area.
This alteration type typically presents highly weathered and soft conditions in the field, making petrographic analysis difficult.
Therefore.
X-Ray Diffraction (XRD) analysis is used to determine the mineral alteration assemblages.
Based on field megascopic descriptions and available samples, the identified mineral assemblages in this alteration are illite, halloysite, smectite, kaolinite, and quartz (Figs.
6 and .
, consistent with the clay mineral alteration assemblages .
Alteration and Mineralization Studies in the Jeblogan area.
Karangtengah (Awang Subang Negar.
DOI : https://doi.
org/10.
33579/krvtk.
Figure 6.
Appearance of Clay Minerals Figure 7.
XRD analysis shows Quartz.
Illite and Halloysite Chlorite Calcite Epidote A Pyrite (Propyliti.
The distinctive feature of propylitic alteration is its greenish color, which is easily recognizable.
In the research area, this alteration type occupies the largest area, approximately 25% of the total research area.
Based on megascopic descriptions and petrographic analysis, propylitic alteration in the research area consists of alteration minerals such as chlorite, calcite, epidote, and pyrite as the primary alteration minerals .
ee Fig.
8 and .
Figure 8.
Appearance of Chlorite.
Calcite and Epidote Minerals KURVATEK Vol.
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e-ISSN: 2477-7870 p-ISSN: 2528-2670 Figure 9.
Petrography analysis shows Chlorite .
G).
Calcite .
D).
Epidote .
C) and Pyrite .
J) Mineralization The alteration and mineralization processes in the research area occurred during the Early Miocene, coinciding with the intrusion of dacite, which generated hydrothermal fluids.
These hydrothermal fluids formed valuable ore mineral deposits in veins trending southeast to northwest.
The valuable metal commodities present in the research area are Gold-Copper-Zinc-Lead (Au-Cu-Zn-P.
in the form of minerals such as chalcopyrite (CuFeS.
, pyrite (FeS.
, sphalerite (ZnS), chalcocite (Cu2S), galena (PbS) and Gold (A.
(Fig.
10 and .
Valuable metal deposits in the research area are found in mineralization veins, including quartz veins, pressure veins, dissemination, and hydrothermal breccias.
Figure 10.
Appearance of Galena.
Sphalerite, and Chalcopyrite .
Alteration and Mineralization Studies in the Jeblogan area.
Karangtengah (Awang Subang Negar.
DOI : https://doi.
org/10.
33579/krvtk.
Figure 11.
Appearance of Chalcopyrite.
Chalcocite and Gold .
Figure 12.
Alteration Map of the Research Area Deposit Type The alteration and mineralization processes in the research area occurred during the Early Miocene.
To determine the characteristics of deposit type in the research area, the author approached key parameters KURVATEK Vol.
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e-ISSN: 2477-7870 p-ISSN: 2528-2670 leading to a specific deposit type, referring to several experts in the field.
Determination of alteration type .
- .
Table 1.
Determination of deposit type .
Characteristics Deposits in the research area Tectonic Setting island arc Genetic Relationship calc-alkaline Igneous Rock dacite, andesite Host Rock Type dome, lava flow, pyroclastic Base Metals Pb.
Zn.
Cu.
Au Au Content Ag/Au Tonnage and Au Grade Deposit Form veins, stockwork, hydrothermal breccias, disseminated Ore Minerals sphalerite, galena, chalcopyrite, chalcocite, pyrite Abundance of Ore Minerals chalcopyrite Gangue Minerals quartz, calcite Mineral Textures crustiform, vuggy quartz, alunite, pyrophyllite, zunyite, sericite, halloysite.
Proximal Alteration illite, smectite, kaolinite, epidote, chlorite, calcite Fluid Inclusions Formation Depth Fluid Characteristics Based on the data obtained from the research, the research area fits the characteristics of a LowSulfidation Epithermal Deposit Type.
This conclusion is based on the tectonic setting of an island arc, the presence of dacite and andesite igneous rocks, the type of host rock .
ome, lava flow, pyroclasti.
, the presence of base metals such as Pb.
Zn.
Cu.
Au, the form of the deposit .
eins, stockwork, hydrothermal breccias, disseminate.
, and the minerals present, including sphalerite, chalcopyrite, galena, chalcocite, and Gangue minerals include calcite and quartz, with textures described as crustiform and vuggy.
The proximal alteration includes minerals like quartz, alunite, pyrophyllite, zunyite, sericite, halloysite, illite, smectite, kaolinite, epidote, chlorite, and calcite.
Additionally, the research area includes areas crossed by faults indicative of a Medium-Sulfidation Hydrothermal Deposit Type, based on the occurrence of minerals such as galena, sphalerite, pyrophyllite, alunite, and zunyite in the faults zone.
IV.
CONCLUSION
The lithology in the research area consists of six rock units, in descending order of age: Arjosari brecciatuff Unit (Late Oligocene-Early Miocen.
Mandalika andesite-lava Unit (Late Oligocene-Early Miocen.
Rohtawu andesite-lava Unit (Early Miocen.
Dacite Intrusion (Early Miocen.
Andesite Intrusion (Middle Miocen.
, and Alluvial Deposits (Holocene-Recen.
The geological structures present in the research area include faults and fractures, with the main controlling fault being a strike-slip fault with a NW-SE orientation.
The research area is divided into four alteration zones: Quartz A Silica A Pyrite (Silici.
Alunite Pyrophyllite A Zunyite A Quartz A Hematite (Advanced Argilli.
Illite Halloysite A Smectite A Kaolinite A Quartz (Argilli.
, and Chlorite Calcite Epidote A Pyrite (Propyliti.
The alteration type in the research area has parameters that match specific deposit types: Tectonic Setting of an island arc.
Igneous Rocks dacite and andesite.
Host Rock Type dome, lava flow, pyroclastic.
Base Metals Au.
Zn.
Pb.
Cu.
Deposit Form veins, stockwork, hydrothermal breccias, disseminated.
Ore Minerals sphalerite, galena, chalcopyrite, chalcocite, pyrite.
Gangue Minerals quartz, calcite.
Mineral Texture crustiform, vuggy.
Proximal Alteration quartz, alunite, pyrophyllite, zunyite, sericite, halloysite, illite, smectite, kaolinite, epidote, chlorite, calcite.
Therefore, the research area is concluded to belong to the Low-Sulfidation Epithermal Deposit Type, with some areas crossed by faults indicative of the MediumSulfidation Hydrothermal Deposit Type.
Alteration and Mineralization Studies in the Jeblogan area.
Karangtengah (Awang Subang Negar.
DOI : https://doi.
org/10.
33579/krvtk.
ACKNOWLEDGEMENTS
The authors would like to thank the Lembaga Penelitian dan Pengabdian Masyarakat (LPPM).
Universitas Pembangunan Nasional AuVeteranAy Yogyakarta for supporting this work.
My grateful thanks are also extended to Mr.
Heru Sigit Purwanto and Mr.
Suprapto for his help in the guidance, i would also like to extend my thanks to Mr.
Galih Imam Priyadi and Mrs.
Wike Rosalina for their support in the site
REFERENCES