Application of Textural Quartz Veins

8/10/2019 Application of Textural Quartz Veins

1/11

-1-

APPLICATION OF QUARTZ VEINS TEXTURES:

EPITHERMAL GOLD TYPE IN SOOKO PROSPECT,

PONOROGO DISTRICT, EAST JAVA, INDONESIA

Mochammad Aziz 1), Emmy Suparka 2)

1) Department of Geology UNSOED,

2) Geology and Palaeontology Research Group, Dept. of Geology ITBe-mail :[email protected] ; [email protected]

ABSTRACT

The study area is located in Sooko, Ponorogo Regency, East Java,

Indonesia; it is dominated by dacite and tuff which have undergone

mineralization and hydrothermal alteration. Several quartz veins are

found. Most of them are characterized by infill- and replacement-

texture, white , yellowish- to brownish-, and spotted look smoky-

colored, compact to slightly brittle, oxidized, contain veinlets of sulphide.

The presence of purple-colored, hexagonal prismatic habit of amethyst

crystals are also noted within some quartz veins.

The assay result for quartz veins averaging between 0.2 0.7ppm Au,

3.3 12.9 ppm Ag with 0.04% Cu, 0.056% Pb, 0.077% Zn, 1.84% As,

0.133% Sb and 0.7% Mo. The study of fluid inclusion giving the

temperature ranging from 216.10C 247.4

0C and salinities 0.9 3,9 eq.

wt.% NaC, relatively low-sulfur- and base metal- content. The presence of

both clay minerals such as illite, halloysite, montmorilonite, jarosite, and

pyrophyllite, as well as several distinct textures include banded-

colloform, crustiform, ghost bladed, vuggy-comb, cockade breccia, and

drusy quartz, indicate low sulphidation epithermal system. Besides,

texturally, the quartz vein system in the study area can be divided into two

superzones: the Crustified-Colloform (CC) - and the Crystalline (X)

superzone.

INTRODUCTION

The study area is part of Southern Mountain of East Java, Indonesia;tectonically it belongs to magmatic arc of Sunda-Banda. Geographically

is located at UTM coordinate of 571.650 mE 573.490 mE and

9.127.630 mN 9.127.690 mN within the exploration area undertaken by

the state company PT. ANTAM Tbk. (Fig. 1). The method which are usedto this study is observation collecting rock samples from outcrop,

especially is quartz vein. The rock samples have been analized using

petrography, PIMA, AAS, and fluid inclusion analysis.


2/11

-2-

Hydrothermal fluid reaction with wall rocks will cause changing inphysical and chemical condition of rocks which is intruded. This

changing include colour, texture, mineral assemblages and permeability.

Whereas the intensities of alteration depend on their hydrothermal fluidcharacteriscs and wall rocks condition. The alteration intensities are also

influence within ore deposits accumulation. So that the intensities of

alteration can be used to determine the accumulation of ore deposits baseon the zonation of hydrothermal alteration.

So that the study of hydrothermal alteration base on the vein texture

characteristic in Sooko, Ponorogo is importance to determine the ore

deposits mineralization in vein epithermal type. The main aims of thestudy is to determine the general textures of vein epithermal and make a

model distribution of texture assemblage. This study is also expected to

be used to identified the texture and zonation, which is usually emplacedby gold mineralization.

GEOLOGICAL SETTING

Physiographically, study area is located in Southern Mountain Zone of

East Java, and tectonically it is belong to Sunda Banda Magmatic Arc.

This arc has been formed since Early Tertier and still active until now.

The magmatic arc is composed by calc-alkaline volcanic rocks andvolcanoclastic interbeded with sedimentary rocks of Paleogen and

Study area

SAMUDERA INDONESIA

Figure 1. Location map of the study area


3/11

-3-

Neogen in age and intruded by andesite, dacite and microdiorite. Theserocks lie over Late Cretaceous rocks. Base on K/Ar dating the Tertiary

magmatism which have related with subduction continental margin can be

devided into two periode, that is Late Eocene Early Miocene and LateMiocene Pliocene (Soeria-Atmadja et al., 1994).

Stratigraphycally, the regional of study area is composed by Oligo Miocene volcanic rocks of Mandalika Formation, Early Miocene Early

Midle Miocene volcanic clastic of Jaten Formation, Late Miocene

volcanic clastic of Wuni Formation, limestone reefs of Wonosari

Formation and Pleistocene young volcanic rocks of Argokalangan (Fig. 2

and 3). Whereas in the study area only Mandalika Formation is found, itis composed by dacitic rocks and tuff. They had been intruded by

andesite, dacite and microdiorite, and had undergone alteration of

prophylitization, and argillitization.

Figure 2. Regional stratigraphy of the study area (Hartono, et al., 1992)

HYDROTHERMAL VEIN DEPOSITS

The hydrothermal fluid can produce mineral deposits in variation shapes

dependent upon the opening of rocks, in which the fluid can pass through.

The mineral deposits have been formed from hydrothermal fluid by cavityfilling deposits or replacement deposits. The replacement process occured

under high - pressures and high - temperatures, near intrusive. Whereas

the cavity filling process occured under low - pressures and lowtemperatures.


4/11

-4-

Cavity filling is deposits which formed from hidrothermal fluid to fill therock openings. Hydrothermal fluids can melt or concentrate forming hot

or cool from magmatic or meteoric, but generally the deposit forms in

hot, dilute and magmatic condition. The first mineral formed from themargin of wall rocks fallowing of rock opening (joint) and developed to

inner part, which generally developed to form dots maker in crystal

surfaces into fluid supply. Cavity filling process can be divided into twoprocesses, firstly to form the rock opening and than followed by

deposition of minerals. Both of these processes work as simultaneous, but

generally they are independent which is separated by a time interval.

Observation of quartz vein deposits in Sooko area, based on theirgeometry and physical characteristics can be divided into three groups of

quartz veins, that is SJU-A, SJU-B and SJU-C but they have same

characteristic (Fig. 4a & b).

The observation of 12 sample out crop in the field show that quartz veindeposits generally as vein deposit zone with 1 4 metre in diameter. They

have density are about 2/m with strike relative to NE SW and dip

direction relative to NW and some to SE. They have characterized bybrownish white to white milky and some are purple (amethyst) (sample

SJU-A3), colourless; spongy; show banded-colloform, smooth banded,

vuggy and some are crustiform with crystal zone (crystal growth), semi

hard and brittle. They content of pyrite, galena, limonite, alterationmineral of zoisite and fluorite. This quartz vein is located in argillic zone.

From the fluid inclusion analysis (using microthermometri method) show

that the quartz vein deposits had been formed at 164.1C 293.2C with

average 216C for SJU-B1, 209.6C - 306C with average 247.4C.

Figure 3. Regional geologic map of the study area

(after modified Hartono, et al., 1992)


5/11

-5-

Mineral which contain fluida inclusion is found in quartz vein withbanding crustifom structure. They are characterized by elongate togranulair crystals, milky white to colourless, but in granulair crystal the

fluid inclusion decripitated; have distribution disseminated spot by spot,

some are oriented forming planar or curve; generally subhedral in shapeand part of these show necking-down , few subhedral to euhedral; 1 5

m; two phase type (liquid and vapour) and sometimes one phase; vapourvs liquid ratio is uniform (Fig. 5). So that, the quartz vein can be

interpreted as epithermal zone with 1,122.76 62.83 metre in depth with

the range of salinity are 0,9%wt 3,9%wt equivalent NaCl, low-sulfur

content and base metal.

From the observation above so that quartz veins in the study area have

horizontal distribution with prediction of longitudinal range to SW or NWabout 600 metre parallel to strike.

Figure 4a. Vein sample map of the study area

Figure 4b. 3D of vein quartz in the study area

Argillic zone

Vein


6/11

-6-

Figure 5. Micrograph sample of fluid inclusion; sample A is SJU-B1, and

sample B is SJU-C3inzet fluid inclusion with forming euhedral-subhedral, planar

and curve; two phase type (liquid and vapour); disseminated

THE TEXTURAL CHARACTERISTICS OF

EPITHERMAL QUARTZ VEIN

Epithermal deposits of Au and Ag commonly have and associated withvolcanic rocks and have been found in quartz vein. Quartz vein is one ofthat have texture zonation, formation pattern and geometry. Factors of

vein deposits formation are mineralization fluid, channel way, host rock

and chemical reaction. 12 samples of slab quartz vein have been analyzed

for megascophic (Fig. 6). They are characterized by the same composer of

material and have resembled of their textures.

SJU-A quartz veins

The observation (megascophic and microscophic) of quartz veinscharacterized by claudy brownish white, massive structures, to start

showing colloform-banded, comb texture and cockade breccia (SJU-A3),

some show vuggy structure and sometime filled by halloisite and quartz,concentration of iron oxide found in the middle and margin of quartz

which marked by brown and yellow colour and become clearer in SJU-A3

to show orientation set parallel. The other characteristic is poruos, some

interlocking of euhedral subhedral quartz crystals and some

intergrowth. Ore deposits consist of galena, metallic grey in colour, cubic,spotted distribution and generally associated with brownish quartz; pyrite

(< 1%), fine grained and iron oxide, sphalerite fine grained (SJU-A3, A4).

Cockade breccia are very clear found in SJU-A4 and vuggy structure isshown in the margin of this vein. In SJU-A5, comb structure become

coarsening forming of euhedral subhedral quartz crystal and iron oxide

which brownish to yellow found only in the margin of vein. In the SJU-A6 have same characteristics with other samples before, but in hear show

off-set of quartz band, and the vuggy structures are oriented parallel,filled by zoisite, illite and iron oxide. The other characteristic of SJU-A7

0 50m

A

0 50m

B


7/11

-7-

is showing a present of ribbon structure, veinlet of pyrite sulphide asoffset layer, ghost bladed texture and the vuggy structure which filled by

montmorillonite, talk together with clay minerals and iron oxide. In SJU-

A7 contain of covelite and others. In SJU-A8 have characteristic same asSJU-A7, but the vuggy structure filled by part of illite and jarosite. Other

characteristic show that the concentration of iron oxide forming

orientation set relatively parallel; due to the border of the crystallin quartzice plane and forming aggregate of quartz grained.

Figure 6. Show of several textural quartz veins in the located area are: A. Colloform; B.

Crustiform and Cockade; C. Cockade; D. Comb; E. Colloform.; F. Crustiform-vuggy

and Bladed; G. Comb; H. Colloform-Amethyst Quartz; I. Zoned crystal quartz; J.

Colloform; K. Saccharoidal; L. Drusy Quartz.; M. Crustiform and Ghost-bladed; N.Comb and Ice Quartz; O. Cockade; P. Crystalline Quartz with spotted galena and clay

minerals

A C DB

M N O

L

P

K

HF

I J

G

SJU A1

E

SJU A4SJU A3

SJU A6

SJU A5

SJU A8SJU A7 SJU B1

SJU B1 SJU B1

SJU C4SJU C3SJU C2SJU C1

SJU B1SJU B1


8/11

-8-

SJU-B quartz veins

The appearance of quartz vein zoned is milky quartz, a little greasy , some

vuggy, fine-grain colloform-banded texture, amethyst are shown in thetop of vein forming band, crystal zoned have begun to be formed which

characterized by drusy quartz and some saccharoidal texture, illite, zoisite

and iron oxide filled partly of rhytmic band of colloform-banded. Quartzvein contain of ore minerals of galena, fine-grained pyrite which

generally associated with brownish quartz, iron oxide concentrade to form

aggregate of quartz grain which show parallel orientation set.

SJU-C quartz veins

The megascophic appearance of quartz veins zoned generally are

brownish white crystalline, massive structure, and show a little joints,begining to see ghost bladed, show crustiform-banded, fine vuggy which

filled by illite and montmorillonite. They contain of fine epidote, iron

oxide, sphalerite, and pyrite (< 1%) (SJU-C1). The iron oxide

concentrated to form aggregate of grain quartz. In SJU-C2, the crystalbegun to form euhedral crystals and the boundary between quartz

crystalline ice with the margin of vein which brownish in colour, containsof fine galena and iron oxide. In SJU-C3, the cockade breccia begun to

see, other appearance is the present of latice bladed and quartz become

coaser. In SJU-C4, the cockade breccia are more clearly to see withbrownish fragment of quartz, the present of comb structure.

Systematic evaluation of vertical and horizontal distribution of textures inthe some epithermal vein give as guidance to develope the zonation

model of texture (Fig. 7 & 8). In study area, the observation of quartz vein

texture consists of seven zonation textures including colloform-banded,crustiform, ghost bladed, vuggy-comb structure, cockade breccia, drusy

quartz, and amorf quartz. They can be divided into two superzone, in

which every superzone is be the boundary by relative position of texture

types and the name of zonation bese on the dominan textures.

- Superzone Crustiform-Colloform (CC), is marked by development of

consistency of banding. The upper zone generally dominated by quartz

amorf and band moss and associate with carbonate and sulphide (SJU-A3,A4, A7, and SJU-C1). Whereas the lower zone is marked by the present

of crystalline band and dominated by quartz amorf (SJU-A3 and SJU-

A4).

- Superzone Crystalline (X), is characterized by crustiform band,

associates with quartz crystalline, sulphide, and carbonate. The quartz

crystalline generally is colourless and prismatic, and saccharoidal quartz

is present spot by spot (SJU-A8 and SJU-B1). This superzone undergone

decreasing of sulphide proportion increasing carbonate crystalline toquartz crystalline downward.


9/11

-9-

Figure 7. Textural zoning of quartz veins and related to distribution gradeof Au-Ag in epithermal vein system-Buchanan Model (1981);

from Morrison (1990) after modified

Figure 8. Mineralization of epithermal veins and related to mineralization

and alteration zone in the located area (vide Buchanan, 1981;after modified)


10/11

-10-

CONCLUSION

Based on the explanation above, the study area can be concluded that:

1. The study area composed by dacite lava of Mandalika Formationwhich occured in Middle Miocene, Quartenary pyroclastic tuff and

quartz vein. Quartz vein in the study area have dimension 600 m in

longitudinal and 2.1 metre in width.2. Almost of all rocks have undergone hydrothermal alteration with

medium to strongly intensity and mineralization.

3. Mineralization which have found in the study area pyrites, galenas,sphalerites, covelites, chalcopyrites, iron oxide, hematite, and

limonite.4. The Au content in the study area is about 0.5 0.7 ppm, with greyish

(smoky quartz) or brownish in colour, whereas in white quartz vein,

the Au content can be predicted up to 0,2 ppm. The Ag content isabout 6.03 ppm.

5. Quartz vein texture characterised by dominantly colloform crustiform banded, cockade breccia, and vuggy comb structure, and

some bladed, porous/spongy which generaly found in vuggy quarz.6. The mineralization environment in the study area probably is low

sulphidation epithermal system.7. Based on the Buchanan Diagram (1981), the study area show that it

have undergone erosion about 228. 82 metre in depth with the

highest elevation now is about 650 metre above see level.8. From the physical characteristic of quartz vein zone, observation of

precious metal mineralization, alteration minerals, and the present of

amethyst minerals and from the fluid inclusion analysis, so that, thestudy area is located in precious metal epithermal vein system zone.

ACKNOWLEDGEMENTS

The authors would like to acknowledge the support and backing of the

management of PT. ANTAM Tbk. Unit GEOMIN who permitted thispaper to be published. Special mention is given to Dean of Faculty ofScience and Technic UNSOED. Additional thanks are given to E. Wiwik

Dyah Hastuti for editing the paper. And memoriam my best lecturer is

given to Prof. Dr. Ir. Totok Darijanto (Mining Department of ITB).

REFERENCES

Bemmelen, R.W. van, 1949, The Geology of Indonesia, Martinus Nijhoff,

The Hague, 732 h.

Corbett, G.J. and Leach, T.M. 1998, Southwest Pacific Rim Gold-Copper

Systems: Structure, Alteration and Mineralization. Society ofEconomic Geologists, USA, Special Publication No. 6, 237 h.


11/11

-11-

Guilbert, J.M. and Park, C.F., JR. 1986, The Geology of Ore Deposits,W.H. Freeman and Company, New York, h. 55-209.

Hartono, U., Baharuddin, dan Brata, K., 1992, Geologi Lembar Madiun,

Jawa, Sekala 1 : 100.000, Pusat Penelitian dan Pengembangan

Geologi, Bandung.

Hedenquist, J.W.; Izawa, E.; Arribas, A.; and White, N.C. 1996,

Epithermal Gold Deposits: Style, Characteristics, and Exploration,

Society of Resource Geology, Resource Geology Special

Publication No. 1, 16 h.

Jensen, M.L., dan Bateman, A.M., 1981, Economic Mineral Deposits,

John Wiley & Sons, New York, Brisbane, Toronto, 593 h.

Lawless, J.V., White, P.J., 1995, Alteration, Brecciation, Veining and

Epithermal Mineralisation, Notes to accompany Lecture Course

for PT. Rio Tinto, Indonesia, Kingston Morrison Limited.

Morisson, G., Guoyi, D., Jareith, S., 1990, Textural Zoning in Epithermal

Quartz Vein, Amira Project P247, Gold Research Group, JamesCook University of North Queensland, 33 h.

Park, C.F., Jr. dan MacDiarmid, R.A., 1970, Ore Deposits, secondedition, W.H. Freeman and Company, San Francisco, 512 h.

Roberts, R.G., Sheahan, P.A., 1985, Ore Deposit Models, GeoscienceCanada, Reprint Series 3.

Roedder, E., 1984, Fluid Inclusions, Review in Mineralogy, Vol. 12,Mineralogical Society of America, Washington, 644 h.

Soeria-Atmadja, R., Maury, R.C., Bellon, H., Pringgoprawiro, H., Polve,

M., dan Priadi, B., 1991, The Tertiary Magmatic Belts in Java, TheProceeding of the Silver Jubilee On The Dynamic of Subduction

and Its Products, LIPI, Yogyakarta, h. 98-121.

Taylor, R.G., 1996, Ore Textures, Recognition, and Interpretation,Geology Department, James Cook University of North

Queensland, Townsville, Queensland, Australia.

Vaughan, D.J., Craig, J.R., 1981, Ore Microscopy Ore Petrography, JohnWiley & Sons, New York, Chichester, Brisbane, Toronto, 406h.

Documents

Application of Textural Quartz Veins