PRIMARY GEOCHEMICAL HALOES IN PROSPECTING FOR GOLD DEPOSITS, UMM RUS MINE, EASTERN DESERT, EGYPT The estimated Au values in the Umm Rus deposit are found to be dependent, besides physico-chemical factors, on the dip angles of the housing fractures and the amount of wedging-out of the quartz veins. The highest values are anticipated in the thin-gently dipping quartz veins which are commonly detected in some parts of level-279/ and level-487/. A stepwise discriminant analysis was used to reduce a number of potential pathfinder variables to an optimum group of pathfinder variables that differentiate between mineralized and unmineralized quartz vein samples. The estimated Au values in the Umm Rus deposit are found to be dependent, besides physico-chemical factors, on the dip angles of the housing fractures and the amount of wedging-out of the quartz veins. The highest values are anticipated in the thin-gently dipping quartz vein GOLD CONTENTS IN RELATION TO GEOMETRIC FEATURES OF QUARTZ VEINS

1. ISSN 1012-5965
DELTA JOURNAL OF SCIENCE 2002, 26:37-53 copyright ©by Tanta Unversity, Egypt
PRIMARY GEOCHEMICAL HALOES IN PROSPECTING FOR GOLD
DEPOSITS, UMM RUS MINE, EASTERN DESERT, EGYPT
HASSAN Z. HARRAZ
Geology Department, Faculty of Science, Tanta University, Tanta 31527, Egypt
(Received: 28 May 2002)
Abstract
The Umm Rus Au-mine area (12 km2
) is, geologically, dominated by a granitoid pluton
intruding gabbroic rocks and affected by tectonic fractures trending NE and NW. The
Au-bearing quartz lodes cut NE-SW principally across the granitoid rocks and
occasionally extend into the gabbros, almost portraying textural features of filling and
deformative aspects. The primary geochemical haloes of Au, Ag, As, Pb, Zn, Cu, Co
and Ni are studied throughout the different mine levels. The distribution of these
elements revealed distinct zonality differences above and beneath the main orebody in
level-487. Zonality in the structure of the haloes is expressed through the exclusive
accumulation of Au and Ag in the intermediate position at level 487. Zinc, Co, and As
haloes exhibit a distinct intensification and expansion with depth. Copper, Pb and Ni
haloes are large and extensive at the uppermost part of the mine. Copper, As, Ni, and
Co accumulate selectively in frontal parts of the haloes. The estimated Au values in the
Umm Rus deposit are found to be dependent, besides physico-chemical factors, on the
dip angles of the housing fractures and the amount of wedging-out of the quartz veins.
The highest values are anticipated in the thin-gently dipping quartz veins which are
commonly detected in some parts of level-279/
and level-487/
. A stepwise discriminant
analysis was used to reduce a number of potential pathfinder variables to an optimum
group of pathfinder variables that differentiate between mineralized and unmineralized
quartz vein samples. Mineralized quartz veins were most effectively discriminated from
unmineralized quartz vein samples on the basis of the Au with Ag selected as less
efficient discriminators. These optimum pathfinders represent the variables that most
effectively differentiate the mineralized samples from unmineralized ones.
INTRODUCTION
During deeply-seated mineralizing processes, the escape and leakage of elementsfrom
the orebody and the channel conducts allow the ore-forming fluids to create a wide
variety of chemical and mineralogical anomalies in the surrounding rocks. These
anomalies are termed epigenetic aureoles (Rose et al. 1979). In many epigenetic
aureoles, the elements change gradually and progressively with location forming
zonation of several scales. Within a mining district, orebodies in different parts of a
district may differ in metal contents or accumulations in a progressive way, commonly
symmetrically around a center. Similarly, ore in large individual orebodies and oreshoots
is commonly zoned laterally and vertically (Rose et al. 1979, p.104).
Zoning in hydrothermal aureoles can also be classified according to directions
(Ovchinnikov and Grigoryan, 1971; Beus and Grigorian, 1977, p.127) into (i) Vertical:
zoning along the direction of flow of the ore-forming fluid, and (ii) Lateral: zoning outward
from ore into wallrock, in a direction normal to the hydrothermal flow direction. At most
orebodies the pattern of zoning is similar, but the extent may differ greatly, and at some
deposits the sequence of elements differs. These chemical and mineralogical aureoles
surrounding the ore and hydrothermal channels provide an enlarged target for
exploration. The available data on these primary haloes allow the outlining of their basic

2. 38 PRIMARY GEOCHEMICAL HALOES IN PROSPECTING FOR GOLD DEPOSITS
features like dimensions, vertical and lateral extent to apply them in exploration of ore
deposits. These features facilitate prospecting for the deeply buried blind orebodies and
have been applied for a number of mineral deposits in the Soviet Union (Ovchinnikov
and Grigoryan, 1971; Rose et al., 1979).
This work describes the morphology and nature of primary haloes of a number
of indicator elements associated with gold vein deposit at the Umm Rus gold mine,
Eastern Desert of Egypt. This study aims to determine the vertical extent of primary
haloes above and beneath gently dipping orebody and to testify whether the hidden
orebody is promising at the Umm Rus mine and to apply them in exploration for Au
deposits. The motivation of this study is to discriminate the mineralized quartz veins
from unmineralized ones and to determine usage of these geometric features as a guide
in exploration for Au-bearing quartz vein deposits.
EXPLORATION HISTORY
The Umm Rus area is located ca 37 km northwest of Mersa Alam on the Red Sea coast
in the central part of the Eastern Desert (Fig.1), covering an area of ca 7 km2
. The area
is well known for its gold deposits which are related to Precambrian rocks. The gold
lode is hosted by granitoid-gabbroic rocks (Fig.1) and was first explored by the Ancient
Egyptians and then exploited by several companies between 1900 and 1907. In 1937-
1938, the deposit has been investigated by "Mines and Quarries Department" (Known
now as the Geological Survey and Mining Authority) who developed the gold mine itself
in 1940 and later during the period between 1943 and 1946 (Fig.3). During this period,
ca 9370 tons of ore lode were mined leaving 6782 tons in situ. Total assured reserves
are 16,000 tons assaying 11 g/t Au (Amin, 1955).
The Umm Rus gold mine has been a target of several current works. Previous
studies (Kabesh et al., 1967; Hilmy et al, 1968; Kochin et al, 1968; Abu El-Ela, 1985;
Kamel et al., 1992; Harraz and El Dahhar, 1993 and 1994; Saad et al., 1996; Arslan,
1999) have described the geologic setting, mineralogy, fluid inclusions of the
mineralized quartz veins and wallrock alteration.
GENERAL GEOLOGY AND MINERALIZATION
The Umm Rus gold mine area comprises varieties of igneous and metamorphic rocks
of Precambrian age. It encompasses metasediments, gabbros and granitoid rocks. The
gabbroic rocks were emplaced into metasediments and intruded by the granitoid rocks.
The granitoid-gabbroic contacts are of a hybrid nature. The Umm Rus granitoid pluton
occupies the middle part of the area (ca 7 km2
) and is bordered NE by Miocene and
Post-Miocene limestone rocks. An age of 573 to 610 Ma is given to the pluton (Hassan
and Hashad, 1990). It is also considered as the early phase of the Egyptian Younger
Granite (Akaad et al, 1979). The gabbroic rocks form thick slightly inclined sheets,
striking NE-SW concordant with the schistosity planes of the metasediments. Abu El-
Ela (1985) and Harraz and El Dahhar (1994) regarded these gabbroic rocks as Younger
Gabbro (Basta and Takla, 1974).
Numerous acidic-basic dykes and quartz veins dissect the Umm Rus granitoid
pluton in a NW-SE, NE-SW and N-S directions and occasionally extend into the
surrounding gabbros through a hybrid zone. Jointing in the granitoid pluton is rather
conspicuous in two main directions trending N8o
-62 o
W and N10o
-28 o
E.

3. 39 Harraz, H. Z.,
Delta J. Sci., 2002, 26:37-53
Fig.1: A simplified geological map of the Umm Rus area
(Modified from Kabesh et al. 1967).
Fig.2: Underground geologic map of the Umm Rus gold mine.

4. 40 PRIMARY GEOCHEMICAL HALOES IN PROSPECTING FOR GOLD DEPOSITS
Main lode
Gold mineralization in the Umm Rus area is localized in, and related to hydrothermal
veins which specify the NNE-SSW and NE-SW fracture systems. The main quartz veins
occur at the southeastern flanks of the granitoid pluton and occasionally extend into the
gabbroic rocks through the hybrid rocks where they pinch out. Other quartz veins cut
principally across the granitoid rocks and pervade throughout the different underground
levels. The majority of the quartz veins are crossed by dykes (Fig.2). Their contacts
against the flanking rocks are commonly sharp, although locally outlined by chlorite,
sericite and ferruginous materials. The veins are formed mainly of massive milky to gray
quartz with or without feldspars, carbonate materials, chlorite and sulfide minerals.
Principal sulfide minerals are pyrite and arsenopyrite. Marcasite, pyrrhotite, sphalerite
and galena are scarcely identified. Gold is reported in the ore lode almost in native form,
as inclusions in pyrite-arsenopyrite or disseminated in sheared quartz aggregates (Amin
1955; Hilmy et al. 1968). The lode is divided by Harraz and El Dahhar (1993) into: (i)
Au-poor, pyrite-quartz vein; (ii) Au-rich, pyrite-arsenopyrite quartz vein, and (iii) gangue
dominant (Fig.2).
The individual quartz veins in the studied gold mine vary from a few centimeters
to >90 cm in width and 3 cm to 5 m in length. The veins usually fill simple fissures of
variable thicknesses (20-35 cm) and enclose some materials of the wall rocks as
screens and breccia. The main quartz vein is of tabular form, locally pinch, swell and
bifurcate into smaller veins, veinlets and stringers (offshoots), and join other veins giving
rise to a network pattern (7m wide). The ore was exploited mainly from the trapping
veins for 200 m along strike and 60 m down dip (Fig.3). These trapping quartz veins
strike N25o
-45 o
E and dip 26o
-70o
NW. The dip of these quartz veins changes from 70
o
NW to 38 o
NW with depth.
MATERIALS AND METHODS
A total of 105 samples were collected from all underground mining levels in the Umm
Rus gold mine (i.e. two shafts and five levels) (Fig.3). All the samples were collected as
chip sample (ca 1 kg) covering an area of ca 1 m2
. The collected samples include 58
samples from the granite-granodiorite rocks and 47 samples from the quartz vein
materials. Samples were split, crushed and then ground to pass 100 mesh.
Silver, Cu, Pb, Zn, Co and Ni were determined by atomic absorption
spectrophotometry (AAS) after HF-HClO4-HNO3 digestion of 1-g samples according to
method used by Tono (1974). Arsenic was determined colourimetrically after KOH
fusion. Gold was determined by a modified technique of Meier (1980) using aqua-regia
solutions and Di-isobutyl ketone extraction. The lower detection limits is found to be 1
ppm for Cu, Pb, Zn, Co & Ni; 0.1 ppm for Au & Ag; and 15 ppm for As. Precision as
observed from relative standard deviations from duplicate analyses was ± 5% for all
elements, except for Au and As where it was ± 12% and ± 14%, respectively.

5. 41 Harraz, H. Z.,
Delta J. Sci., 2002, 26:37-53
Fig.3: A location map showing sites of samples collected from different levels of
mining activity in the Umm Rus gold mine.
Table 1: Concentration ranges and statistical distribution parameters for some selected
trace elements (in ppm) in granitoid and quartz veins at the Umm Rus gold mine.
Elements Clarke*
n Range Mean Median Cb S t
Granitoid Rocks
Au 0.004 50 <0.1- 5.8 1.05 1.02 0.36 0.5624 0.66
Ag 0.04 52 <0.1- 2.2 0.44 0.37 0.26 0.5798 0.51
As 1.5 52 25 - 270 80 74 33 0.6840 98
Pb 16 58 1.5- 51 13 11.5 7 0.3982 20
Cu 10 58 1.2- 53 9 8.2 4.1 0.5794 16
Zn 39 56 5.4-152 48 43 18 0.5146 74
Co 1 58 1.4- 23 12 8.8 5.1 0.3806 14
Ni 4.5 56 3 - 158 18 14 8.8 0.3143 17
Quartz vein
Au 32 <0.1- 10.2 2.9 2.27 0.95 0.5899 2.05
Ag 33 <0.1- 5.1 1.3 1.12 0.54 0.6457 1.67
As 40 36 - 395 144 130 59 0.7701 171
Pb 40 5.2- 86 21 17 15 0.3591 27
Cu 47 1.2- 55 10 8 6 0.6204 19
Zn 45 12 - 195 68 65 37 0.7364 101
Co 47 3.2- 101 14 12 9 0.3088 17
Ni 47 9.5- 59 18 15 12 0.5067 28
*: After Beus and Grigorian (1977). Cb: Local background values.
S : Geometric standard deviations. t : Threshold value (Cb x S 2
).

6. 42 PRIMARY GEOCHEMICAL HALOES IN PROSPECTING FOR GOLD DEPOSITS
DISTRIBUTION OF ELEMENTS
Range and arithmetic means of the different elements in the granitoid rocks and quartz
veins materials collected throughout the different underground levels in the Umm Rus
gold mine are given in Table 1 and frequency distributions are shown in Fig.4. Initial
inspection of chemical analyses shows that unlike the granitic rocks, the quartz veins
are enriched in Au, Ag, As, Pb, & Zn contents and depleted in Co & Ni. The ranges of
Au, As, As, Pb, and Zn contents in the granitic rocks are less abundant relative to the
quartz veins, while Co & Ni contents in the granitic rocks are relatively higher than in
the quartz veins. This is reflected in the shape of the distribution curves (Fig.4) and in
the values of the distribution parameters (Table 1). The shape of the histograms
indicates approximately bimodal lognormal distribution for Au, As, As, Pb, and Zn and
unimodal normal distribution for Co & Ni.
The distribution parameters (Table 1) were determined mathematically after log
transformation of the raw data and excluding samples showing visual high
concentrations of the investigated trace elements following procedure of Lepeltier
(1969). It can be seen that, the background levels of the Au, Ag, and As are 20 times
higher than the corresponding Clarke values (Table 1). The locally high background
levels and variation of Ni and Co are most probably related to the surrounding gabbros
rather than to mineralization.
Fig.4: Frequency distribution of some selected trace elements in subsurface materials at the Umm
Rus gold mine. (Granitoid rocks, n = 58; Quartz veins, n = 47).

7. 43 Harraz, H. Z.,
Delta J. Sci., 2002, 26:37-53
TRACE ELEMENT RELATIONSHIPS
The trace elements in the granitoid rocks and quartz veins are summarized in
correlation matrices (Fig.5). The majority of elements in all sample media are positively
correlated, except Co and Ni which show negative correlation with most of the elements
studied. These results demonstrate that Au is strongly correlated with Ag, As, and Pb
and weakly correlated with Zn and Cu. The As showed extremely strong correlation with
both Au and Ag, thus emphasizing that the arsenopyrite is the main Au carrier in the
Umm Rus mineralization (Harraz and El Dahhar, 1993; Saad et al., 1996). Arsenic, Pb
and Zn have a significant inter-correlation, which are bound to the ores. On the other
hand, Au has a weak correlation with Cu due to scarce occurrence of Cu-bearing
minerals. Positive correlations were also obtained between Ni and Co. These element
pairs are not directly related to the ores, as shown by the lower negative correlations of
the ore-associated elements.
From the above mentioned relationships and results (Fig.5), the variables can
be classified into two haloes: i) Au, As, Ag, Zn and ii) As, Pb, Zn ± Cu.
Although some elements are common to the two haloes, other are
characteristic of only one. These haloes are consistent with paragenetic sequences
previously established in the Umm Rus gold mine (Harraz and El Dahhar, 1993).
Fig.5: Significant correlation levels for the Umm Rus granitoid rocks and gold-bearing quartz veins.
GEOCHEMICAL MAPS
Geochemical mapping based on the primary haloes of some selected trace elements
is illustrated in subsurface geochemical contour maps (Fig.6). These geochemical maps
revealed large and extensive haloes of the elements around the quartz veins (Fig.6).
Co and Pb appear to have the narrow haloes and rarely extend beyond the quartz veins.
Unlike the primary haloes of Pb, Cu and Ni the primary haloes of most of elements are
restricted laterally distance from the mineralized zone (Fig.6). These anomalies are of
epigenetic nature because they are superimposed on the pre-existing country rock. Au,
Ag, As, and Zn elements have their highest contents in the quartz vein materials (see

8. 44 PRIMARY GEOCHEMICAL HALOES IN PROSPECTING FOR GOLD DEPOSITS
Table 1), which decrease with increasing distance from the quartz veins. The primary
haloes of Au and Ag form distinct bands in conformity with the shape of the quartz veins.
Gold and Ag exhibit a distinct haloes occupying the central parts of the mine at level
487/
, where the quartz vein body wedges out at deeper levels (Fig.7C). Moreover, in a
vertical section there is a very marked upward shift in the haloes produced by As, Zn
and Co, relative to the particular halo of Au.
Zonality in the structure of the haloes is expressed through the exclusive
accumulation of Au and Ag in the intermediate position of level 487/
. Zn, Co, and As
haloes exhibit a distinct intensification and expansion with depth. Cu, Pb and Ni haloes
are large and extensive at the uppermost part of the mine (Fig.6). Cu, As, Ni, and Co
accumulate selectively in frontal parts of the haloes, whereas the maximum
concentration of Au, Ag, and Zn are especially characteristic within the area of the
mineralized quartz veins.
Fig.6: Geochemical contour maps showing the distribution of Au, Ag, As, Pb, Cu, Zn, Co, and Ni
in the country rock samples collected throughout the different underground mining workings in
longitudinal cross section in the Umm Rus gold mine (refers to Figures 2 and 3).

9. 45 Harraz, H. Z.,
Delta J. Sci., 2002, 26:37-53
CONTRAST OF GEOCHEMICAL ANOMALIES
To compare the relative usefulness of some elements as pathfinders for mineralization,
contrast of anomalies were calculated (Table 2). The conventional methods of defining
contrast of anomalies usually involve dividing the anomalous concentration by the
threshold or background values (Levinson 1980, p.215; Beus and Grigorian, 1977,
p.51). However, this does not allow positive and negative anomalies to be compared
on an equal basis. Hence, the contrast values (Table 2) were calculated according to
the method adopted by Pirie and Nichol (1981), which depends on whether a positive
anomaly (enrichment) or a negative anomaly (depletion) exists. The Au, Ag, As, Pb,
and Zn show great variation in their contrast values. Considering the thickness of
primary dispersion haloes (Table 2), Au, Ag and As are of great utility as pathfinder
elements for the mineralization. Pb and Zn come next in their importance as guide
metals.
To quantitatively evaluate the vertical zoning, the linear productivity values of
the haloes and zoning contrast coefficients have been calculated throughout the
different mine levels (Table 3). This coefficient represents the relationship of the value
of pair elements in level-279/
and level-540/
. The coefficients showed their maximum
significance for Zn and As and minimum-significance for Co. It is obviously noticed that
the linear productivity is a quantitative expression of the relative accumulation of an
element in each level (Fig.7). This permits separation of the elements into three groups
including: (1) As, Zn and Co, characterizing deep horizon of the deposit (level-540/
), (2)
Pb, Cu and Ni, characterizing the uppermost horizon of the deposit (level-279/
), and (3)
Au and Ag characterizing the central part of the orebody (level 487/
) (Fig.7).
Table 2: Dispersion and geochemical contrast of certain trace elements in
primary haloes in the Umm Rus gold mine.
Element
Width of
dispersion
related to
mineralization
(in meter)
Geochemical Contrast*
Main
shaft
Western
shaft
Level
279/
Level
487/
Level
540/ Average
Au 2.37 101 78 69 100 64.0 83
Ag 1.82 50 32 34 50 23.0 38
As 1.50 68 56 6.5 9.4 9.3 30
Pb 1.18 56 7.7 44 26 12.0 29
Cu 0.77 45 9 14 12 9.3 18
Zn 0.98 16 14 32 26 22.0 22
Co 0.50 9.6 7.8 7.6 5.1 25.0 11
Ni 0.68 5 5.2 1.9 2.8 9.3 4.8
* After Pirie and Nichol (1981) where:
Geochemical contrast = [Maximum concentration - Minimum concentration]/ Minimum
concentration

10. 46 PRIMARY GEOCHEMICAL HALOES IN PROSPECTING FOR GOLD DEPOSITS
Table 3: The values of the halo linear productivity elements (in meters.
percent) and ratios at the Umm Rus gold mine.
Elements
Pairs of
elements
The Linear productivity of
elements and ratios Zoning
Contrast
Coefficient*Level
279/
Level
487/ Level 540/
Au 0.00241 0.00450 0.00225 0.93
Ag 0.00069 0.00254 0.00061 0.88
As 0.10040 0.18400 0.32740 3.26
Pb 0.01850 0.01168 0.01074 0.58
Cu 0.01698 0.00914 0.00227 0.13
Zn 0.02864 0.07300 0.09427 3.29
Co 0.00795 0.00201 0.01456 1.83
Ni 0.00836 0.00419 0.00318 0.38
Ag/Au 0.00083 0.00167 0.00049 0.58
As/Au 0.09123 0.13802 0.28146 3.09
Zn/Au 0.02047 0.06356 0.07417 3.62
Co/Au 0.00610 0.00269 0.02672 4.38
Pb/Au 0.01537 0.01062 0.00535 0.35
Cu/Au 0.01045 0.00749 0.00190 0.18
* The zoning contrast coefficient is obtained by dividing the linear
productivity of elements or ratios of level 540/
over those of level 279/
.
Fig.7: Variation of linear productivity of elements with depths in the Umm Rus gold mine.
By using the contrast values and the widths of the primary haloes, the lateral
and vertical changes can be established (Table 4). The pattern of zoning in Umm Rus
gold mine in the lateral and vertical directions is rather similar to the known well
established ones in worldwide orebodies (Rose et al., 1979). However, the extent of
changes in the study haloes may differ greatly owing its existence to slight difference in
temperature and pressure of the fluid as well as the chemical properties of elements.

11. 47 Harraz, H. Z.,
Delta J. Sci., 2002, 26:37-53
Table 4: The lateral and vertical zoning of the primary halos in the Umm Rus gold
deposit.
Lateral Zoning *
Vertical Zoning **
Au, Ag, As, Pb, Zn, Cu, Ni, Co Pb, Cu, Ni, Au, Ag, As, Zn, Co
* Elements are given in decreasing order of width of their halos; for example,
Cobalt has the narrowest halo whereas gold has the extensive.
** Reading from the left to right, the indicators of the supra-ore parts grade
or pass downward to the indicators of the sub-ore parts of an ore zone.
To reduce a number of pathfinder variables, a stepwise discriminant analysis was
used initially on all samples to distinguish mineralized samples from unmineralized
ones. Since the discriminant analysis produce requires that variables used in analysis
approach a normal distribution, all elements were log-transformed. The discriminant
analysis was performed by SPSS-programme (Norusis, 1993). Using a stepwise
produce, various combinations of elements were studied and it was found that a good
discrimination was obtained with Au and Ag. These two elements met the minimum F-
to enter requirements (i.e., F-values >2.3) for the stepwise procedure. The discriminant
function is given as:
D = 3.232Au – 0.657Ag + 0.028
A calculated F-value 160.49 for testing equality of individual multivariate group-
means for above elements is highly significant at the 99% level. Overall correct
classification rate 94.29%, with rates of 100% and 87% for the mineralized and
unmineralized samples, respectively. Including additional variables does not
significantly improve classification. Histogram of discriminant scores for the two groups
(Fig.8) show the efficiency of discriminant function is far higher than for any single
element. Variability is considerably reduced and multivariate normality has been
achieved. Therefore, the discriminant function was found to be appropriate for use in
the evaluation of mineralization of the Umm Rus gold mine.
Fig.8: Histograms of discriminant scores. Elements used in
discriminant equation: Au and Ag. Arrows indicates group means.

12. 48 PRIMARY GEOCHEMICAL HALOES IN PROSPECTING FOR GOLD DEPOSITS
GOLD CONTENTS IN RELATION TO GEOMETRIC
FEATURES OF QUARTZ VEINS
The variation of Au-contents with the changing of the geometric features of the quartz
veins (i.e., dip angles and thicknesses) as well as depth are plotted in Figure 9. The
relationship between these variabilities was examined to discriminate between the
mineralized quartz veins and unmineralized ones and to determine usability of these
geometric features as a guide in exploration for-Au-bearing quartz vein deposits.
Based on the data presented in fig. 9A, the Au-content shows a progressive
decrease with increasing amounts of the dip angle of the quartz veins. A significant
negative interrelationship between Au-contents and dip angles of the quartz veins exists
(r = -0.73). The high Au-contents appear to be preferentially concentrated in the gently
dipping parts the quartz veins rather than the steeply ones (Fig.9A). Dip angles of the
quartz veins inversely correlated with the depth of mineralization (r = -0.43) (Fig.9D).
The gently dipping quartz veins were localized in some parts of level-279/
and level-
487/
(i.e. 10-22 m) where the highest Au-contents were detected at these levels (Fig.9
D &E).
According to the available data, it seems that the Au-contents have a weak
correlation with the thicknesses of the quartz veins (r = 0.21). The highest Au-contents
are mostly found in the thin parts of the quartz veins particularly at level-279/
and level-
487/
(thickness ranging from 18 cm to 30 cm) (Fig. 9 B & C). Unlike the thin quartz veins,
the thick ones are frequently found at surface outcrop and at the uppermost parts of the
mine. Meanwhile, the more thinner quartz veins (<18 cm in diameters) are recorded in
the deeper horizons of the underground mining workings (Fig.9C). The thick and thin
quartz veins seldom contain gold (Fig.9B). The decrease in thicknesses of the quartz
veins with increasing depth (r = -0.72), is not strictly related but seem to be due to the
thicknesses of pre-existing fractures and wedging out of the quartz veins with depth.
Inspection of the Au-contents in the investigated deposit reveals that it depends
almost exclusively on the geometrical features of the quartz veins. It was anticipated
that the high Au-contents should be restricted to the thin-gently dipping quartz vein
samples (i.e., 18 cm to 30 cm wide and 25o
--35 o
NW dip).
Based on the aforementioned binary relationships between Au-contents and
the depth of mineralization as well as geometric features of the quartz veins (dip angles
and thicknesses) (Fig.9), some ternary relationships such as: dip angle-depth-
thickness, depth-dip angle-Au content, dip angle-Au content-thickness, and Au content-
thickness-depth were constructed as shown in Fig. 10. Although all these ternary
relationships are potential discriminating between the Au-bearing quartz veins and
barren ones and clarifying the characteristic features of both types, yet the dip angle-
Au content-thickness ternary plot is the most appropriate one (Fig.10).
DISCUSSION
The primary geochemical haloes around the Au-bearing quartz veins at the Umm Rus
gold mine are of plutonogenic epithermal classes of late epigenetic ores. Such
anomalies are most extensively developed near the Au-bearing quartz vein at level-279/
and channel-ways at level-487/
, because of the low viscosity of the mineralizing fluids.
The latter might have imparted to local addition of As, Co, and Zn in the flanking wallrock
and leaching of elements along portions of the path of the ore-forming fluid (Harraz and
El Dahhar, 1993, 1994). As many other epigenetic ores and aureoles, the tested
elements change gradually and progressively in the Umm Rus mine (Table 4) as a result
of changes in the ore-forming fluids and the condition of deposition.

13. 49 Harraz, H. Z.,
Delta J. Sci., 2002, 26:37-53
.
Fig.9: Vertical relationships between: (A & B) Au content in the quartz vein samples collected from
the different underground mining workings and both of the dip angles and thicknesses of the
quartz veins; (C & D) depth and both of the dip angles and thicknesses of the quartz veins; and
(E) Au content in the quartz samples from the different underground mining workings and depth.
Correlation coefficient "r" compared to the critical value "c = 0.4648" at the 99% confidence level
is indicated. (Number of samples = 47).

14. 50 PRIMARY GEOCHEMICAL HALOES IN PROSPECTING FOR GOLD DEPOSITS
Fig.10: Ternary relationships between Au-contents in the quartz vein samples collected from the
different underground mining workings and different geometric features of the quartz veins in the
Umm Rus gold mine. Dotted line discriminate between thick and thin quartz veins; Dashed line
discriminate between steep and gentle dipping quartz veins; and solid line discriminate between
mineralized and unmineralized quartz veins.
(A) Faces of tetrahedron.
(B) Section of the tetrahedron parallel to the basis 10*Au-thickness- dip Angle at 50% depth
of mine (representaive for level 487 and 540).
Abbreviations: T = thick, Th = thin, S = steep, G = gentle, M = mineralized; and UM =
unmineralized.
The metals in the Umm Rus gold deposit showed vertical zonation. The
anomalous aureoles of the Au and Ag do match well with the morphological features of
the quartz veins at the central part of mine the (Level 487/
). Zn, As and Co have their
highest concentrations and widest haloes along the feeding structures beneath the main
orebody, while the Cu, Ni, and Pb are almost developed above or (completely above)
the orebody.
Structurally, the distribution of the primary geochemical haloes indicates that
the vertical zoning is caused by "displacement" of the halo fields in the direction of the
wedging out of the main quartz veins. Au and Ag haloes are the most displaced ones
and almost seen as a board and intensive "Cap" in the area of wedging-out of the quartz
veins. Unlikely, the As, Zn and Co haloes are the least displaced and have the minimum
thickness and intensity. Consequency, in a vertical section, there is a marked upward
shift in the haloes of As, Zn and Co, compared to the Au haloes. It is expected that the
contrast of halo zoning of these elements becomes evident with the complete
disappearance of the haloes field of high Au and Ag concentration in level-540/
, where
the As, Zn, and Co haloes are the highest. This may imply that the Au-bearing quartz
veins at the Umm Rus gold mine completely disappear in deeper horizons of the mine
beneath the main quartz veins located at level-487/
. The presences of economic gold
deposit is expected in the uppermost levels of the mine, a matter which is not recorded

15. 51 Harraz, H. Z.,
Delta J. Sci., 2002, 26:37-53
in the studied samples (Fig.7D). The extremely high volatile elements (e.g. As)
concentrated beneath the mineralized zone indicate a deep level of erosion of
geochemical anomalies and rocks in the area. This might permit carrying panning and
stream sediment surveys to detect Au placers in the drainage patterns dissecting the
mineralized zone and the nearby areas.
CONCLUSIONS
The following conclusions are drawn from the primary geochemical haloes around the
Umm Rus gold deposit:
1) The results showed that the greatest contrast between the quartz veins and the
granitic rocks are Au, Ag, As, Pb, and Zn (enriched in quartz vein materials),
and Co & Ni (depleted in quartz vein materials).
2) Statistical studies show the significant variation in the background values of the
investigated metals. Au, Ag, and As have exceptionally high background levels
which reflect close association of Ag and As with the Au-mineralization in the
area.
3) Inter-element relationships reveal significant positive correlation between Au
and As, Ag, Pb & Zn. The best correlations are those between Au-Ag, Au-As,
and Ag-As.
4) Au, Ag, As and Zn are of great utility as pathfinder elements for Au-
mineralization. However, the zoning contrast coefficients based on the linear
productivity confirm that Zn, As and Au are the most useful pathfinders for
mineralization.
5) The linear productivity is quantitatively an expression of the relative
accumulation of the elements in each level that permits separation of the
elements into three groups: (a) As, Zn and Co group, characterizing the deeper
horizon of the deposit (i.e., level-540), (b) Pb, Cu and Ni group, characterizing
the uppermost horizon of the deposit (i.e., level-279/
), and (c) Au and Ag group
characterizing the intermediate position at level 487/
.
6) The relationship between Au-contents and geometric features of the quartz
veins as well as depth of mineralizations can be used as a guide to
hydrothermal quartz vein mineralizations. The ternary relation dip angle-Au
content-thickness is of particular importance. These ternary relationships are
sufficient to discriminate between the mineralized quartz veins from those
unmineralized ones.
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