Porphyry Copper in Kerman Region, SE-Iran;

A metallogenic Interpretation

Morteza MOMENZADEH

N e m a t o l l a h R A S H I D N E J A D

Geological Survey of Iran

P.O. Box 13185-1494, Tehran-IRAN�

Tehran: 1989

Abstract

The Kerman porphyry Copper stocks including Sarcheshmeh are the

roots of stratovolcanoes which their tops are cut by erosion. The

mineralization is genetically related to the subaerial Plio-Quaternary

volcanism which extends NW-SE wards diagonally along the whole

country from Caucasus to Pakistan borders.

In the Kerman region some stratovolcanoes including Sarcheshmeh,

Meduk, Kuhpanj, etc. are eroded enough to expose the porphyry

mineralizations. Some volcanoes, mainly in the southeastern part of the

Kerman region are completely eroded. So that, any probable prophyry

mineralizations are eroded away. The presence of ore occurrences on the

top of some almost not eroded stratovolcanoes, like Mozahem and

Bidkhan is probably the witness of porphyry mineralization at depth.

Introduction

The metallogeny of porphyry copper deposits, including the Sarcheshmeh

deposit, SE-Iran is briefly discussed (Figure 1). The region is a NW-SE

extended quadrangle of 350×50 Kilometers, which is a sector of a diagonal � Geological survey of Iran. P.O. Box 13185-1494, Tehran/ Iran, 1989.

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NW-SE Iranian copper belt (Orumieh- Dokhtar). The latter itself is a part of

Alp-Himalaya copper belt.

Figure 1: Location map of Kerman copper region

Petrology of the enclosing rocks

The Ores are hosted by three rock types:

1. The Eocene acid to basic pyroclastics and lavas; the intermediate rocks

are dominant and the pyroclastics are several times more than lavas.

2. The Miocene and Plio-Quaternary intrusives, subvolcanics and dykes;

Intrusives occur mainly in southeast and are granodiorite, quartz-

diorite,granite and diorite. The subvolcanics occur mainly in northwest.

They vary from granitic to dioritic and from dacitic to andesitic in

composition. Dykes are frequent in the entire area. They are diabasic, dacitic

and rhyolitic in composition.

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3. Plio-Quaternary volcanoes, volcanic domes and dykes; They are

composed of dacite, andesite and andesite-basalt.

All three rock types are petrochemically identical, hence may be

derived from a dioritic to quartz-dioritic magma.

Tectonics

The NW-SE folds and faults in northwestern part and N-S faults in

southeastern part of the region are the dominant structural parameters.The

intrusives, subvolcanic bodies and the chain of volcanoes have also a NW-

SE trend. The tectonic movements, as well as igneous activities in Plio-

quaternary times have been more intensive than those of Eocene-Miocene

times.

Mineralization

Some 120 copper and copper-gold deposits and occurrences and a few Pb,

Zn, Cu deposits are known in the Kerman region (GSI, 1973).Concerning

the enclosing rocks and the manner of emplacement the deposits are of two

categories:

1. Ores occurring merely in Eocene rocks, with no apparent relation to the

intrusives, dykes and volcanoes; They are of disseminated, massive, vein and

veinlet types, but strata bound and occasionally stratiform (Figure 2).

Surface alteration occurs around orebodies.

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Figure 2: Schematic showing of Eocene lava and pyroclastic layers with

stratiform- syngenetic copper reconcentrated copper in fractures (stratabound ore)- in

Kerman region.

2. Mineralization in and around subvolcanic bodies, or close to the

vents and at aureoles of volcanoes; Extended hydrothermal alteration,

besides surface alteration is developed around ore bodies .Alteration zoning

in many deposits from center to peripheries (potassic to propyllitic) is

traceable. Mineralogic zoning is also well developed in some deposits (Cu,

Mo to Cu, Pb and Zn from center to peripheries). Pyrite is the major

sulfide in all cases. The Sarcheshmeh porphyry copper- molybdenum fall in

this category, (Waterman and Hamilton, 1975).From 120 ore deposits 31 are

porphyry copper (GSI, 1973). Besides copper, molybdenum is common. Zn-

Pb occur commonly at peripheries of orebodies, especially in fractures

outwards from porphyry stocks (Figure 3). Gold and silver are associated

with porphyry copper and vein type Pb-Zn-Cu.

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Figure 3: Scheme showing an eroded volcano (Bare- Ahmad) with week porphyry Cu-

Mo and vein type Pb, Zn mineralizations at its aureoles (Ghanatmarvan deposit). No

scales

Metallogenic interpretation

The Kerman region as a sector of the "Orumieh-Dokhtar" Tertiary

tectono-volcanic zone has been an active volcanic belt since, a t least,

Early Eocene times. During Eocene the volcanic activity occured mainly in

submarine environment in a NW-SE basin. The products of volcanism, i.e.,

pyroclastics, lavas, and ore forming fumaroles, with Fe, Cu, Pb, Zn, H2S,

etc. have been introduced into the basin from submarine volcanic centers,

like volcanoes, and produced syngenetic- volcanogenic- stratiform

disseminated and massive? ores (Figure 4 III).

From Miocene on the igneous activity, with a culmination in Plio-

Pleistocene times continued in subaerial environment. A chain of NW-SE

subaerial volcanoes subvolcanics and intrusive stocks are the products of

that activity. The hydrothermal solutions carry upwards metal ions from

magmatic sources and/or from barried syngenetic ores of Eocene rocks,

mobiled by igneous activities (Figure 5).

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Figure 4: Illustration of magma intersection with atmosphere (I) lithosphere (II) or

hydrosphere (III); Porphyry type, Vein type and Kuroko or stratiform Cu, Mo, … deposits

can be formed respectively.

Figure 5: Schematic figure showing the two options of sources for porphyry copper in

Kerman region; 1) Young (pliopieistocene) magma. 2) Remobilized syngenetic

copper in paleogene hostrocks. A combination of the two options is also expected.

The solutions before exposing to air, due to decrease of temprature and

pressure, and changes in.physico-chemical conditions discharge and

precipitate metals (sulfides) in lower parts of the stratovolcanoes and make

up a tentative porphyry orebody. When the peak of such volcanoes, is eroded

their minerallized root has been exposed as a porphyry orebody. The

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discrimination between a subvolcanic stock and the root of a stratovolcano

which its peak is eroded is not easy. Therefore it is probable that many of

stocks, known as subvolcanics are indeed remains of eroded stratovolcanoes.

In the case of Sarcheshmeh and Lachah (Meduk) porphyry deposits there are

many criteria, which show that they are indeed the roots of stratovolcanoes

For example in the Sarcheshmeh area (Bazin and Hubner 1969) the

presence of mineral water springs and dyke networks, as well as the young

eruptive rocks (Kuhe- Amiralmomenin) indicate that Sarcheshmeh

porphyry copper stock is an eroded stratovolcano (Figures 6 and 7). Many

other porphyry deposits, like Darrehzar, Kuhpanj, Bidkhan, Sarkuh and

Bare-Ahmad are likely similar to Sarcheshmeh deposit. The vein type

copper indications on top of some stratovolcanoes, like Mozahem and

Bidkhan can be a witness of porphyry copper at the roots of these

stratovolcanoes (GSI, 1973).

Figure 6: Geological map of Sarcheshmeh deposit. App. Scale, 1:55,000 (After D.

Bazin & Hubner, 1969, GSI. Rep.13)

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Figure 7: Schematic section of Sarcheshmeh porphyry stock. The morphology of

Sarcheshmeh stratovolcano is reconstructed.

Conclusion

The porphyry orebodies are entirely emplaced in Eocene volcanic

sequence, which itself is the host of the syngenetic copper ores. Therefore

it is always probable that a volcano intersects a syngenetic ore zone below

surface. If so the ore forming materials may become mobile and contribute

in the formation of the epigenetic porphyry ores (Figure 5). But it is too

soon to discriminate the share of syngenetic Eocene copper and that of

epigenetic Plio- Quaternary magmatic copper in the formation of porphyry

copper in Kerman region. A contribution of both sources is not out of

question.

About the bottom and the top of a porphyry copper stock (Sillitoe, 1973)

it is important to note that; due to a decrease in temprature and pressure the

metallic ions on their way from the earth's interior to the surface in a volcanic

center will precipitate sequentially from depth toward the crater. Hence

each metal will fall in a definite depth. The continuous flow of fumaroles

from depth to the surface guarantees a continuous supply and precipitation of

metal (Figure 8). One can compare the volcano's vent with a filtering

channel with a row of filters for Cu, Pb, Zn, etc. (Figure 8).

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Figure 8: Circulation of fumaroles from magma outside occurs through the volcano vent

(a) The vent acts like a filtering tube (b) in which physico chemical filters absorb different

elements.

If the channel is closed from the upper end (Figure 4 II) the filtering

process do not work perfectly. This case happens when magma and its

fumaroles intersect the lithosphere. This filter model explains well why a

porphyry stock becomes poor in copper content towards top and bottom. If

the proposed metallogenic model is correct the strategy of prospection for

porphyry copper in Kerman region has to be revised. It is then critical to

look for stratovolcanoes, enough eroded to expose the proper depth of

porphyry mineralization and discriminate them from subvolcanic intrusive

stocks. The frequency of volcanoes and subvolcanic stocks in the

northwest and intrusives in the southeast of the Kerman region may be

explained by the fact that the Plio-Quaternary volcanism becomes younger

north- westwards and the erosion level becomes deeper-- towards the

southeast and the intrusives may be considered to be the roots of

completely eroded volcanoes.

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References

1. BAZIN, D. and H. HUBNER (1969)

Copper deposits in Iran, Geol. Surv. of Iran.

2. GSI (1973)

Institute for Geological and Mining Exploration and Exploration for ore

deposits in Kerman Region, Geol. Surv. Of Iran, Rep.

Yu/53, 246 p, 1 map.

3. SILLITOE, R.H, (1973)

The tops and Bottoms of Porphyry Copper Deposits. Econornic Geology, vol.

68, pp. 739-815.

4. WATERMAN, G.C. and R.L. HAMILTON (1975)

The Sarcheshmeh Porphyry Copper Deposit. Economic Geology, Vol. 70, pp

568-576.