Download Origin of gypsum formations in copper deposit of Murgul, NE Turkey

Origin of gypsum formations in copper deposit of Murgul, NE Turkey
Ali Sait
a
Çol ,
Nevzat
b
Özgür ,
Tuğba Arife
b
Çalışkan
aSuleyman
Demirel University, Graduate School of Applied and Natural Sciences, Isparta, Turkey
bSuleyman Demirel University, Faculty of Engineering, Department of Geological Engineering, ısparta, Turkey
ABSTRACT
The Anayatak and Çakmakkaya orebodies forming the Cu deposit of Murgul in the East Pontic metallotect, NE Turkey were completed before supergene alteration and erosion occurring in short periods of time under subaerial
conditions in the area. Furthermore, pyroclastics and sediments (up to 10 m) in the Cu deposit of Murgul represent the short time interval as marker bed. It is an important element for the terrestrial conditions dominated in the
area. The local identifier marker bed with ore under atmospheric conditions at the surface, sedimentation dacitic pyroclastics and alteration is interpreted as the result of the erosion events. Gypsum formations located on the
upper level of the formerly existing Bognari orebody refer to a brecciated bearing mineralization formed under atmospheric conditions. In this last case gypsum formations can indicate an environment by oxidation of sulfide
minerals associated with atmospheric conditions, unlike some of the research results. In Çakmakkaya orebody, gypsum minerals found in altered dacitic pyroclastics are genetically different from above described gypsum
minerals. The origin of gypsum minerals can be attributed to seawater sulfates reduced by Fe-oxide/-hydroxide phases. Gypsum minerals in pyroclastics of Anayatak and Çakmakkaya orebodies are not related to host rocks
ore mineral assemblage and must be considered as prior to sulfide mineral assemblage. Later on, investigation area exposed to tectonic uplift and subsequent Cu deposit of Murgul formed under terrestrial conditions.
1. INTRODUCTION
Massive sulfide deposits in the East Pontic metallotect, NE Turkey, which extends over an area of more than 350 km E-W and 60
km N-S, are associated with altered 150 to 300 m thick dacitic pyroclastic host rocks in Senonian age1,2. In the area, the
important base metal deposits change along the general strike from east (Cu>>Pb+Zn; type Murgul) to west (Pb+Zn>>Cu; type
Madenköy and Lahanos) (Figure 1 and 2)3. Genetically, Cu deposit of Murgul and other massive sulfide deposits in the east of
the metallotect can be classified to the subvolcanic-hydrothermal type with a Senonian island arc volcanism under predominant
subaerial conditions and represent a transition between Kuroko type deposits and copper porphyries. In comparison, the Cu
deposits of Madenköy and Lahanos in the west are related to a submarine-hydrothermal activity in a volcano-sedimentary
sequence under temporally subaquatic conditions. In Cu deposit of Murgul, the mineralization is hosted in dacitic pyroclastics
with a thickness up to 300 m. These pyoclastic host rocks in the study area are overlain by a 20-50 m thick formation cosnsisting
of pyroclastics, sandstones and limestones which is overlain by 500 m thick barren dacitic lava flows. The gypsum minerals in
the above mentioned 20-50 m thick formation, which must have been formed under subaerial conditions, might be generated
with respect to the oxidation of sulfide minerals in the ınvestigation area respectively. A few researchers4,5 such as assume that
Cu deposit of Murgul can be assigned to a submarine-hydrothermal origin under subaquatic conditions with respect to the results
of 34S analyses. Therefore, the aim of this research is to elucidate the origin of gypsum minerals in the sequence consisting of
pyroclastics, sandstones and limestones due the results of 34S.
Table 34S values in dacitic pyroclastic host rocks of the Cu deposit
of Murgul.
Figure 6. 34S values of the Cu deposit of Murgul
in comparison to other genetical equivalent
deposits9,10.
4. CONCLUSIONS
Figure 1. Geologic setting and location map of the East
Pontic metallotect. 1: Murgul, 2: Madenköy, 3: Lahanos. .
Figure 2. Simplified lithostratigraphic column of the East
Pontic metallotect. LBS: Lower Basic Series; LDS: Lower
Dacitic Series: UBS: Upper Basic Series: Cu: Base metal
Deposits.
2. MATERIAL AND METHODS
In the copper deposit of Murgul and environs, a detailed study was performed by Özgür (1985), Çağatay and Eastoe (1995),
Özgür et al. (2008) and Abdioğlu et al. (2015) from the view of geochemical and isotope geochemical points3,5,10,11. Gypsum
minerals, which are located within the dacitic pyroclastic host rocks9.10 . and form the main topic of this study, were collected, to
clarify the genesis of the copper depsoit of Murgul (Figure 3) Firstly, the existence of gypsum minerals could be confirmed by the
XRD investigations additionally (Figure 4). Later on, 34S analyses were realized in the Isotechs Laboratories (Illionis, USA)9 .
Figure 3.Gypsum mineral from the Çakmakkaya
open pit of the copper deposit of Murgul.
.Figure 4. XRD diagram of the gypsum mineral from the
<çakmakkaya open pit of the Cu deposit of Murgul.
3. RESULTS
3.1 Geologic setting
The Cu deposit of Murgul occurs within the upper part of the first volcanic cycle and is associated with a 150 to 300 m thick
group of felsic pyroclastic rocks whose upper contact is marked by a thin layer of marine sediments, and is characterized by
intense erosion and weathering6. The pyroclastic host rocks can be classified into Senonian age according to paleontological
observation and overlain by interbedded pyroclastic tuffs, sandstones and limestones, and by 200 to 500 m thick barren dacitic
lava flows7. The pyroclastic host rocks consist of altered breccias and tuffs. The primary minerals in the altered host rocks can be
observed only as relicts. In the less altered host rocks, the fluidal groundmass contains phenocrysts of plagioclases (An28-35) and
quartz and plagioclase microlites (An12-30), relicts of hornblendes and biotites, and minor quantites of apatites, sphenes and
haematites 2.
The massive sulfide deposits in the East Pontic metallotect are assigned to 150-300 m thick dacitic pyroclastics in
Senonian age. In the east of the metallotect, there is a ration of (Cu >> Pb + Zn; type Murgul), there is a ratio of (Pb
+ Zn >> Cu; type Lahanos and Madenköy) in the west. Genetically, Cu deposit of Murgul and other massive sulfide
deposits located in the east can be classified to the subvolcanic-hydrothermal type with a Senonian island arc
volcanism under predominant terrestrial conditions and represent a transition between Kuroko type and copper
porphyries. The mineralization in the Cu deposit of Murgul is asociated with dacitic pyroclastics with a thichness up
to 300 m. In the study area, this proclastic sequence is overlain by 20-50 m tuff-sandstone-limestone formation and
500 m thick barren dacitic lava flows. The dacitic pyroclastic sequence with a thickness up to 300 m in which Cu
deposit of Murgul is located has been altered intensively in the last stage of the first volcanic activity. Massive sulfide
desposits have been emerges as a result. Hyrothermal alteration may be classified as (i) advanced argillic and
phyllic alteration as first phase and silicic alteration as last phase. The formation of the Anayatak and Çakmakkaya
orebodies forming the Cu deposit of Murgul must have been completed before supergene alteration and erosion
occurring in short periods of time under atmospheric conditions in the area. Furthermore, pyroclastics and
sediments (up to 10 m in the Cu deposit of Murgul) represent the short time interval as marker bed. These are an
important element for the terrestrial conditions dominated in the area. The local identifier marker bed with ore under
atmospheric conditions at the surface, sedimentation dacitic pyroclastics and alteration is interpreted as the result of
the erosion events. Gypsum lens is located on the upper level of the formerly existing Bognari orebody refers to a
brecciated bearing mineralization formed under atmospheric conditions. Here gypsum formations can indicate the
environment by oxidation of sulphide minerals associated with atmospheric conditions, unlike some of the research
results. In Çakmakkaya orebody, gypsum minerals found in altered dacitic pyroclastics are different in genetical
comparison to above described gypsum minerals. The origin of gypsum minerals can be attributed to sea water
sulfate reduced by Fe-oxide/-hydroxide phases. Gysum minerals in pyroclastics of Anayatak and Çakmakkaya
orebodiees are not assoc contained within the dacitic pyroclastics Çakmakkaya mass mineralization assemblage is
not any relationship with the mineralization occurred prior to mineraliziated with sulfide mineral assemblage and
must have been formed prior to sulfide mineral assemblage. Later on, investigation area exposed to tectonic uplift
and subsequent Cu deposit of Murgul formed under terrestrial conditions. The intensively altered dacitic pyroclastic
host rocks in Senonian age are overlain by less altered barren dacitic lava flows. There, the mineralization does not
pass the marker bed between host rocks and barren dacitic lava flows. It shows that the mineralization has been
completed before supergene alteration and erosion together with the formation of the barren dacitic lava flows.
Dacitic pyoclastics as host rocks show some similarities with “ore-related brecias”. This indicate surficial brecciation
in the Cu deposit of Murgul and environs which can be occur by repeated volcanic activities providing required
temperatures in the system, because there are contemporaneous formed volcanic domes in a few hundred meters
distance which prove the above mentioned brecciation. Although Porphyry Cu deposits and Cu deposits of Murgul
have some similarities in terms of the model of the hydrothermal alteration, there are some important differences: (i)
high-grade ore is generally located in the center of ore body, (ii) when Murgul bed investigated the alteration does
not appear potassic alteration zone and (iii) Murgul at a location fairly close to the surface mineralization is must
have occurred.
.
5. ACKNOWLEDGEMENTS
This study has been supported financially by the Scientific Research Coordination Office within Suleyman Demirel
University under contract number 2511-M-2011 and 3680-YL2-13.
6. REFERENCES
3.2 Hydrothermal alteration and mineralization
The Cu deposit of Murgul is mainly mined in the two open pits of Anayatak and Çakmakkaya3. The mineralization within the Cu
deposit of Murgul is associated with a two-stage hydrothermal alteration of pyroclastic host rocks 2,8: (i) an initial stage of phyllic
and argillic alteration, and (ii) a late stage characterized by silicification (Figure 5). The first stage led to the destruction of the
primary paragenesis of the pyroclastic host rocks and the replacement by quartz and pale green to greasy sericite. An extensive
but poor mineralization of disseminated pyrite. and chalcopyrite of type 1 2,6. There is a rather sharp contact between phyllic and
argillic zones with up to 3 m wide spheres. The phyllic alteration zone is surrounded by a pervasive argillic alteration zone
composed of quartz, montmorillonite, dickite, illite, pyrite and chalcopyrite. The late stage is characterized by silification consisting
of quartz replacement of the volcanic host rocks producing cryptocrystalline jasper.
Mineralized veins and veinlets (type 2 and 3) crosscut the altered pyroclastic host rocks. The both ore types can be interpreted to
be a later phase of ore remobilization which was generated during the last episode of volcanic activity. During this time period
mechanical disintegration took place, opening faults and fissures for ascending ore-bearing solutions resulted in the formation of
the stockwork-like mineralization (type 2). Finally, the latest open-space fillings (type 3) suggest ore mineralization closely below
the terrestrial surface.
3.3 Isotope geochemistry
3.3.1 Ore minerals
In 17 samples of pyrite, chalcopyrite and sphalerite + galena
within the Cu deposit of Murgul and environs, 34S analyses were
realized for this study10 (Figure 6). Due to 34S values, the Cu
deposit of Murgul has been compared with excellent studied Cu
deposits such as Kuroko type deposits, Cyprus type deposits and
copper porphyries. Accordingly, the Cu deposit of Murgul
represent a transition between Kuroko type deposits and copper
porphyries.
3.3.2 Gypsum minerals
In the orebody of Çakmakkaya within the Cu deposit of Murgul, we
have collected three samples of gypsum minerals. Firstly, the
purity of the samples of gypsum minerals were re-examined by xray diffractometer in which the samples show gypsum minerals in
100 percent9,10. 34S analyses of gypsum minerals from
Çakmakkaya orebody promote and range from 18,6 to 18.8
‰(Table 1). These 34S values were compared with values ranging
from 20,0 to 20,8 ‰5 and between 20,3 and 20,4 ‰11
corresponding to 34S values of sulfate of modern ocean waters
which range from 20,0 to 21,0 ‰. The both researcher5,11
associate the origin of gypsum minerals to the seawater sulfate
reduced by Fe-Oxide/hydroxide phase in altered volcanic host
rocks.
Figure 5. Hydrothermal alteration zones of
the Cu deposit of Murgul9,10.
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