Stream Sediment Geochemical Exploration for Gold in theKazda¤ Dome in the Biga Peninsula, Western Turkey
HÜSEY‹N YILMAZ
Dokuz Eylül Üniversitesi, Mühendislik Fakültesi, Jeoloji Mühendisli¤i Bölümü, Buca, TR–35160 ‹zmir, Turkey(E-mail: [email protected])
Abstract: The Tuztafl› Au-Ag mineralized system was discovered within the Kazda¤ dome using BLEG (bulk leachextractable gold) and 180-µm stream sediment geochemical data collected across the Biga Peninsula in westernTurkey. The deposit is located within the hinge of an antiform consisting mainly of high-grade metamorphic andmélange rocks that include the Alt›noluk Pb-Zn-Cu-Ag-Au and Evciler Fe-Au-Cu deposits on the southern and onthe northern flanks, respectively; no mineralization has been reported prior to this work which was first carriedout in 1996 between Alt›noluk and Evciler. The BLEG Ag/Au ratios at Tuztafl› (max 87) and Alt›noluk (max 43) arevery high to extremely high demonstrating the area to be relatively Ag-rich. This Ag enrichment is furtherdemonstrated by rock chip Ag/Au ratios reaching up to 43 at the Tuztafl› deposit. Silver is a moderate to veryeffective pathfinder for Au at Tuztafl›. Arsenic is useful, being more mobile than Sb. Arsenic also constitutes themost coherent and the most significant geochemical anomaly in the northern half of the AYALE (Ayvac›k-Alt›nova-Evciler) area which is underlain mainly by the mélange rocks intruded by granitoid. The BLEG samplingaccompanied by further follow-up 180-µm stream-sediment sampling is a powerful technique in detecting Au-Agdeposits or occurrences. BLEG appears to be a time- and cost-efficient stream sediment geochemical technique fordiscovering relatively large primary geochemical halos encompassing the precious (Au, Ag) and base metal (Cu, Pb,Zn) deposits.
Key Words: BLEG sampling, geochemistry, gold, mineral exploration, Kazda¤, western Turkey
Biga Yar›madas› Kazda¤ Domundaki (Bat› Anandolu)Dere Sediman› Jeokimyasal Alt›n Aramalar›
Özet: Tuztafl› mineralizasyon sistemi Biga Yar›madas›nda Kazda¤ domunda (Bat› Anadolu) BLEG (alt›n›n hacimselayr›flt›r›lmas›) ve 180-µm dere tortulu jeokimyasal verilerini kullanarak keflfedilmifltir. Yatak ço¤unlukla yüksekdereceli metamorfik ve melanj kayalar›ndan oluflan bir antiform s›rt›nda yer al›r ve s›ras›yla bu antiform güney vekuzey kanatlar›ndaki Alt›noluk Pb-Zn-Cu-Ag-Au ve Evciler Fe-Au-Cu yataklar›n› da kapsar; fakat ilk olarak 1966 dayap›lan bu çal›flma öncesinde literatürde Alt›noluk ve Evciler aras›ndaki bir cevherleflmenin (Tuztafl› cevherleflmesi)varl›¤›ndan söz edilmemifltir. Tuztafl›ndaki BLEG Ag/Au (maksiumum 87) ve Alt›noluk (maksiumum 43) oranlar›n›noldukça yüksek oluflu sahan›n göreceli Ag-zengini oldu¤una iflaret eder. Bu Ag zenginleflmesi 43’e kadar ulaflankayaç Ag/Au oranlar›yla da gösterilir. Gümüfl Tuztafl›ndaki Au’›n aranmas›nda oldukça etkin bir iz bulucudur.Antimondan daha hareketli olan As alt›n aramas›nda keza yararl›d›r. Arsenik granotoid sokulumlu melanjkayalar›nca altlanan çal›flma alan›n›n kuzey yar›s›ndaki en tutarl› ve en önemli jeokimyasal anomaliyi oluflturur. BLEGörneklemesini takiben yap›lan180-µm dere sediman› Au-Ag yatak ve zuhurlar›n›n bulunmas›nda güçlü bir tekniktir.BLEG, k›ymetli (Au-Ag) ve baz metal (Cu, Pb, Zn) yataklar›n› çevreleyen göreceli büyük ilksel jeokimyasal halelerinaranmas›nda zaman ve maliyet aç›s›ndan etkin bir dere tortulu jeokimyas› tekni¤i olarak gözükür.
Anahtar Sözcükler: BLEG örneklemesi, jeokimya, alt›n, maden arama, Kazda¤›, Bat› Anadolu
Turkish Journal of Earth Sciences (Turkish J. Earth Sci.), Vol. 16, 2007, pp. 33-55. Copyright ©TÜB‹TAK
33
Introduction
Systematic collection and analysis of drainage samples hasbeen established as method of mineral exploration at boththe reconnaissance and detailed scales in many parts ofthe earth (Ottesen & Theobald 1994). Obtainingmaximum efficiency from a geochemical explorationprogram necessitates a balance between minimizing the
density of sampling/maximizing the length of thedetectable dispersion trains and significantly reducing thecost/time requirements (Cohen et al. 2005). Even whencare is taken to obtain representative samples, goldexplorations can vary markedly as a result of varyinghydraulic processes in the stream and the differentresponses of high- to low-density minerals during
STREAM SEDIMENT GEOCHEMICAL EXPLORATION FOR GOLD
34
transport (Nichols et al. 1994). Furthermore, slightchanges in the slope of a stream bed, coupled with theparticle scarcity effects on sample representativity maylead to the inhomogeneous Au distribution. Therefore,BLEG stream sediment sampling is considered as analternative technique to that of 180-µm stream sedimenttechnique to overcome the problem of erratic golddistribution. BLEG appears to be the best way to doreconnaissance-scale sampling for Au.
Western Turkey has been a focus of exploration forgold deposits in the last two decades. However, althoughgeochemical surveys form a major part of mostcompanies’ strategies, little information is available on thegeochemical dispersion of elements from deposits andprospects in western Turkey by which survey design maybe optimized. The extraction of gold from large samplesis a common approach that improves samplerepresentativity and reduces detection limits; such as thebulk leach extractable gold (BLEG) method, described byElliot & Towsey (1989), Radford (1996) and Y›lmaz(2003).
The study area selected for investigating thedispersion characteristics of various elements is located50 km SE of Çanakkale and is accessible by theÇanakkale-Edremit highway (Figure 1). This area iscontained within the Ayvac›k-Alt›nova-Evciler (AYALE)structural dome where extensional features are cut byseveral NE-trending intrusions. The Kazda¤ dome hostsnumerous mineral occurrences and deposits (Figure 1).Three of these deposits, representing a range of deposittypes and differing levels of emplacement, have beenincluded in the study area. The first, the Alt›noluk(Papazl›k) Pb-Zn-Cu-Ag-Au deeper-polymetallicepithermal (?) vein deposit with a resource of 240 K tonsgrading 5 g/t Au and 25 g/t Ag, is located in the southernpart of the area and has been intermittently exploitedduring the last century (MTA– Mineral Research andExploration Institute of Turkey 1966, 1993). The seconddeposit, re-discovered during this study, is the Tuztafl›epithermal Au-Ag deposit where numerous small ancientworkings were recognized. The third deposit is theEvciler (Ayazma) Fe-Au-Cu proximal-skarn deposit in thenorthern margin of the Kazda¤ structural mountainrange, which was exploited in ancient times (Y›lmaz &Kara 1996). The area between the Evciler and Alt›nolukareas was not known to contain gold and silvermineralization until this study (Y›lmaz & Kara 1996).
K›l›ç et al. (2004) reported that Au values ranging upto 14 ppm in soil and 3 ppm in silicified dacitic toandesitic volcanic lava dome rocks aroundK›rantepe/K›sac›k village 13 km east of Ayvac›k. Aydal etal. (2004) also noted the presence of gold anomalies inthe silicified zones of ultramafic rocks at Alakeçili.
This study evaluates the effectiveness of the BLEG(bulk cyanide leach extractable gold) technique and aquaregia-digested metal contents of the 180-µm (-80 #)fraction of stream sediments as well as the 180-µm (-80#) fraction of soil at AYALE, particularly in the Tuztafl›area, which is underlain by metamorphic rocks andmélange. The purpose of this study is to demonstrate theefficiency of the BLEG technique in exploring for gold asa case study rather than investigating the detailed geneticrelationships among these three deposits with probabledifferent levels of emplacement.
Regional Geology at AYALE
The AYALE is located in the southeastern part of theKazda¤ Mountain range (Figure 1), which forms astructural and topographic dome of high-grademetamorphic rocks (Schuling 1959; Bingöl 1969; Okayet al. 1991, 1996). The Kazda¤ range trends NE–SWand, rising to 1767 m above sea-level, forms atopographic anomaly in the northeastern Aegean, wherethe average elevation is below 500 m. The Kazda¤ Groupforms a doubly plunging, NE–SW-trending anticliniorium(Duru et al. 2004). The Ezine Group, over three-km thickand containing systematic occurrences of carbonate rocksin the greenschist facies, represents a fragment of theRhodopian passive margin, a consequence of Permo–Triassic rifting of the future Maliac/Meliata Ocean, alsoobserved in Greece. The emplacement of the Denizgörenophiolite over the Ezine Group occurred during theBalkanic orogeny, a major compressional event, whichaffected the whole Rhodope area, and was characterizedby northward nappe emplacement during Jurassic–EarlyCretaceous times (Beccaletto & Jenny 2004).
Basement rocks in the Tuztafl› area consist ofPalaeozoic gneiss, marble and amphibolite (Okay & Sat›r2000), tectonically overlain by a highly deformed, LateCretaceous to Palaeocene oceanic accretionary mélangecomprising basalt, clastic sediments, limestone andserpentinites (Figure 2); the sequences are separated bythe Alakeçili-Akp›nar shear zone. The Kazda¤ Massif, theshear zone, and the accretionary mélange are intruded by
H. YILMAZ
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STREAM SEDIMENT GEOCHEMICAL EXPLORATION FOR GOLD
36
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Figure 2. Geology (Okay & Sat›r 2000) and mineralization map of Tuztafl› area (this study).
Late Oligocene/Early Miocene granitoids (23.8 Ma:Delaloye & Bingöl 2000). The Alakeçili-Akp›nar shearzone of strongly mylonitized gneiss and serpentinite, 2-km thick, occurs between the Kazda¤ Massif and theaccretionary mélange in the north (Okay et al. 1991). TheAkp›nar fault is interpreted as a low-angle detachmentwhich juxtaposes brittly deformed upper crustal rocksover the ductilely-deformed mid-crustal rocks (Okay &Sat›r 2000). The Evciler granitoid is an elliptical, calc-alkaline pluton situated north of the Kazda¤ range(Figures 1 & 2). The granitoid extends northeast–southwest parallel to the trend of the Kazda¤ dome andthe Akp›nar shear zone. Its mineralogical compositionranges from monzodiorite through quartz diorite togranodiorite and the latter is the predominant faciesconstituting over 70% of the pluton (Öngen 1978, 1994;Genç 1998; Yücel-Öztürk et al. 2005). In the north thegranitoid has intruded the Late Oligocene–Middle Mioceneandesites, dacites and intercalated sedimentary rocks.These volcanic rocks are geochemically similar to theEvciler Pluton and are regarded as its extrusiveequivalents (Genç 1998). Thermal metamorphismdeveloped at the contacts between the Late OligoceneEvciler Granodiorite (Yücel-Öztürk 2005) and marbleand/or metamorphic rocks hosting gold mineralization(Y›lmaz & Kara 1996).
The Evciler, and several other I-type, medium toshallow-seated intrusive rocks of granite/granodiorite tomonzodiorite compositions were emplaced into basementof the Kazda¤ Group. Early Miocene volcanism within theEvciler area is characterized mainly by andesite and dacitelavas, and associated pyroclastic rocks (Genç 1998)whereas dacitic lava domes, lava flows and volcanoclasticsare dominant facies in the Alt›noluk area. The Evciler(Ayazma) Fe-Cu-Au, the Tuztafl› Au-Ag and Alt›noluk(Papazl›k) Pb-Zn-Cu-Ag-Au mineralized systems (Figure1) occur within Kazda¤ mountain range which is regardedas an extensional metamorphic core complex of Oligoceneage, consisting of gneiss, marble and amphibolite at itsfootwall, and Early Tertiary accretionary mélange withexotic Upper Cretaceous eclogite blocks in its hangingwall (Okay & Sat›r 2000; Duman et al. 2004; Beccaletto& Jenny 2004; Beccaletto & Steiner 2005).
Local Geology and Mineralization at AYALE
Alt›noluk-Papazl›k Prospect
Information on the geology and mineralization ofAlt›noluk (Papazl›k) base and precious metal deposit
(Figure 1) is almost nil except for MTA inventories (MTA1966, 1993). The Alt›noluk vein-type Pb-Zn-Ag-Aumineralization is hosted by a sheared marble layerintercalated with amphibolite and gneiss of the Kazda¤metamorphic rocks. The thickness of the veins reaches1.6 m over a strike length of several hundred meters.The ore consists predominantly of coarse crystallinegalena, sphalerite, and pyrite with minor chalcopyrite andcovellite. The Alt›noluk mineralization forms a small-tonnage ore body (240 K tons) with grades of 8.2% Zn,6.7% Pb, 5 ppm Au and 25 ppm Ag (MTA 1966, 1993).
Evciler-Ayazma Prospect
The Au concentration reported first at Evciler isassociated primarily with massive pyrite-marcasite-pyrrhotite-chalcopyrite-quartz-calcite mineralizationwithin marble and biotite amphibole gneiss intruded bythe Evciler Pluton (Y›lmaz & Kara 1996). The Evciler(Ayazma) Fe-Cu-Au mineralization occurs mainly asexoskarn consisting predominantly of prograde garnetand diopside with minor retrograde tremolite, epidote,chlorite, scapolite and sericite. Mineralization appears tobe strongly controlled by the intercalated amphibolegneiss and marble contact which is cut by a porphyriticgranodiorite sill of the Evciler pluton. A central core ofmineralization with a 200 m strike length containinghigh-grade gold concentrations has intermittentlyoutcropping, N50°E-trending lensoidal extensionstowards the east (250 m) and west (500 m). The Au- andassociated pyrite-pyrrhotite mineralization appears to becontrolled by a NE-trending structure, dipping at 50°NW(Y›lmaz & Kara 1996). Best rock chip results to datereturned up to 14 ppm Au at 4 m with several othervalues above 4 ppm.
Based on earlier Au-exploration work (Y›lmaz & Kara1966), a detailed study of the Evciler skarn alterationwas carried out by Yücel-Öztürk et al. (2005). Theysuggested that the geochemical characteristics of theÇavufllu monzodiorite, Karaköy granodiorite andmesocratic Evciler rocks were similar to averages for Au-Cu and Fe-skarn granitoids, whereas the geochemicalcharacteristics of the leucocratic Evciler rocks weresimilar to averages for Sn- and Mo-skarn granitoids. TheEvciler granitoid is also characterized by relatively un-evolved to moderately evolved and oxidized suites, as inmost Au-Cu core metal associations globally (Yücel-Öztürk et al. 2005). They concluded that ‘composition
H. YILMAZ
37
and petrologic evolution of Evciler pluton have had theprimary controls on skarn alteration, mineralization andmetal content such as Cu, Au and Fe’, despite the fact thatthere was either no analysis carried out for Cu and Au orno reference cited on Cu and Au mineralization in theirstudy.
Tuztafl› Prospect
The Tuztafl› prospect and its surrounding area areunderlain mainly by Kazda¤ metamorphic rocks includinggneiss, marble and amphibolite, and Çetmi mélangeconsisting of basalt, greywacke, siltstone, chert,limestone, serpentinite and eclogites, which are cut by theLate Oligocene/Early Miocene Evciler granitoid andandesites (23.8 Ma; Delaloye & Bingöl 2000). TheTuztafl› prospect, underlain by fine- to medium-grainedgneiss and the Evciler pluton, contains threeapproximately N50°E-trending and 20° to 40°N-dippingquartz veins (Figure 3). Several additional Au-bearingquartz veins are recorded over a strike length of 8 kmtoward the southwest. However, east-southeast ofK›rcalar the trends of the quartz veins vary betweenN70°E and N60°W (Figure 2). The drusy crystalline tosaccharoidal quartz vein/breccia with vug-infill, comb andminor crustiform textures at the Tuztafl› prospectcontains native Au and Ag, pyrite and arsenopyrite. Thequartz veins, encompassed by a strong to weak argillic-silicic alteration halo of 600 m by 2500 m, have amapped strike length of 1200 m, an average width ofabout 6 m, and reach a maximum width of 12 m. Theargillic alteration within or around the quartz veins isrepresented by illite/sericite. Preliminary fluid inclusionanalysis (40 Th °C measurements) of two samplesindicates mineralization temperatures of 213 °C and 233°C with salinities of 0.7 and 1.7 wt% NaCl equivalent.Fluid inclusions are typically irregular in shape and rangein size from 10 to 100 µm and averaging 40–50 µm.Quartz textures, clay mineralogy and limited fluidinclusion results may indicate an epithermal style of Au-Ag mineralization. Ancient workings associated withearthy slag piles were also located along the quartz veinin the prospect area.
Exploration Geochemistry
A metamorphic core complex within the Kazda¤metamorphic dome stretches from Ayvac›k to Evciler and
is intruded by several NE-trending granitoids. This areawas selected for the first orientation surveys on the useof exploration geochemistry including BLEG, 180-µm (-80#) stream sediment and 180-µm soil geochemicalsampling for discovering precious occurrences at AYALEin Turkey. The two deposits are 20 km apart and noprecious metal mineralization between the deposits hasbeen reported prior to the BLEG geochemical sampling bythis study.
Climate, Topography and Regolith
AYALE has a semiarid-type climate with dry summers andcold, wet winters. July and August are the hottest monthswith average temperatures around 30 °C whereasJanuary and February are the coldest with temperaturesaround -5 °C. Annual rainfall is 700 mm. The landscapeat AYALE is dominated by ENE–WSW-trending first-orderriver valleys which are the surface expression of the~E–W-trending grabens. Mountains, particularly in theTuztafl› prospect area reach 800 m. Further north andsouth the topography is smoother and gentler with amaximum altitude of 250 m around the Evciler andAlt›noluk areas. Major perennial rivers, such as BayramiçÇay›, begin in narrow valleys and further west flow withina major graben; however, the majority of the streams areephemeral. Hills in the AYALE are covered mainly by pineforest. Cultivation is restricted to olive groves on thesouth and fruit on the north because of lack of largevalleys.
Weathering of the metamorphics and granites isgenerally shallow, with deeper weathering along faultsand other structures. Neutral-pH grassland soils consistof a dark A-horizon overlying lighter-coloured parentmaterial, which in turn underlain by B-horizon soils,include concretions and earthy accumulations of calciumcarbonate. The soil material transported into the drainagesystem consists mainly of illite, quartz and metamorphicdetritals with considerable organic substances and minorFe-Mn oxides.
Sampling and Analysis
Sample points were selected from published 1:100,000scale topographic maps to achieve a sampling density of 1sample per 6–7 km2 (Figure 3). A two-man teamconsisting of one geologist and one sampler collected anaverage of 15 samples per day. Active stream sediment
STREAM SEDIMENT GEOCHEMICAL EXPLORATION FOR GOLD
38
H. YILMAZ
39
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Regional BLEG and 180-µm Survey in AYALE Area
Reconnaissance BLEG sampling carried out in the AYALEarea yielded anomalous values ranging from 0.6 to 15.2ppb Au and 0.1 to 190 ppb Ag (Figure 4). Table 1contains the summary statistics for three variables.Skewness coefficients for raw data indicate that alldistributions are positively skewed. Although BLEG Au atthe 95th percentile level appears to represent the veryanomalous values and is more or less similar to those ofAu-Ag threshold1+2 values (Table 1), log-transformedBLEG Au and Ag threshold1+2 values are slightly higher forAu and 2.6 times lower for Ag. Therefore, the decisionwas made to work with log10-transformed values of thedata instead of the raw values, which reduces theasymmetry of the distribution as indicated by theskewness coefficient (log). The log-transformation hashelped the reduce skewness in all cases but a very smallpositive skewness usually remains.
The BLEG anomalies were followed up using 180-µmstream sediments. These samples yielded weak to verystrong Au, Cu, Pb, Zn, As, and Sb anomalies (Table 2,Figure 5) with peak values of 285 ppb Au, 14 ppm Ag,130 ppm Cu, 1280 ppm Pb, 1250 ppm Zn, 253 ppm Asand 121 ppm Sb. In twenty four of the 585 180-µmstream sediment samples Au, Ag, Cu, Pb, Zn, As and Sbvalues are greater than 23 ppb and, 5, 70, 54, 133, 65and 18 ppm, respectively, for the 95th percentile. Thesevalues are indicative of moderately anomalous metalcontents. The threshold1+2 values derived from the rawdata (Table 2) are 2 to 6 times higher than those derivedfrom the log-transformed data. As indicated by the rowdata, all distributions are slightly to moderately positivelyskewed whereas distributions appear to be symmetric atlog-transformed data, although a small positive ornegative residual skewness usually remains. Results ofthe180-µm stream sediment sampling indicate threecoherent clusters of anomalous Au-Sb-As-Cu values(Figure 5). The clusters of major Au and Sb anomaliesexhibit similar dispersion patterns and appear to beperipheral to the cluster of extensive As anomalies. Rock-chip sampling from quartz veins with minor sulfides,particularly in the Tuztafl› prospect area, shows Au valuesup to 5.4 ppm, with 42 samples greater than 0.5 ppm Auand 30 samples greater than 1 ppm Au (Table 3, Figure6). Negligible Au is detected within samples containingore grade Cu, Pb and Zn. This may indicate that Au issituated within quartz rather than sulfide minerals. An
association of Ag with Au in quartz veins is demonstratedby relatively high values (up to 130 ppm Ag) within As-rich zones. However, no correlations occur between Au-Ag and As (Table 5). Antimony is generally weakly andlocally (south of Evciler) strongly anomalous and has asimilar dispersion pattern to that of Au in 180-µm streamsediment samples at this location. Stream samples exhibitcoherent and very strong As anomalies, overlapping thoseof Au. Lead and Zn anomalies are generally weak but verystrong in two isolated locations. They are overlapped bythe As dispersion patterns.
The 180-µm soils at the Tuztafl› Prospect weresampled over an area of 1 km2 at a line spacing of 100 mwith samples at 25 m along lines (Figure 7). The 180-µmsoils contained values ranging from 25 ppb Au. This correlates well with As. To the east, anarea 400-m long and 150-m wide is defined by >25 ppbAu. Another smaller soil gold anomaly to the southeast,occurring between XL2 and XL12, has dimensions ofabout 50–150 m x 1000 m. The first and the second soilAu anomalies overlap with the As anomaly. A moderate tostrong soil As anomaly in an area 50-200 m by 1800 m(between XL1 and XL17) returned As values generally
H. YILMAZ
41
STREAM SEDIMENT GEOCHEMICAL EXPLORATION FOR GOLD
42
Figure 4. BLEG sample location and Au, Ag and Cu assay results from Ayvac›k-Alt›nova-Evciler (AYALE) area.
Table 1. Statistical values for the 1.18 mm BLEG geochemical data set of the AYALE area.
Elements Au Ag Cu Au Ag Cu
Data Raw Log-transformed
Minimum 0.1
STREAM SEDIMENT GEOCHEMICAL EXPLORATION FOR GOLD
44
Tabl
e 2.
Stat
istic
al v
alue
s fo
r th
e 18
0-µm
str
eam
sed
imen
t ge
oche
mic
al d
ata
set
of t
he A
YALE
are
a.
Elem
ents
AuAg
CuPb
ZnAs
SbAu
AgCu
PbZn
AsSb
Dat
aR
awLo
g10-
trra
nsfo
rmed
Min
imum
<1
<0,
5<
1<
1<
9<
1<
10.
0-0
.30
0.00
0.00
0.95
0.0
0.0
Max
imum
280
14.0
013
012
8012
5025
312
12.
41.
142.
113.
113.
102.
42.
1
Mea
n5
1.26
2526
7721
100.
3-0
.30
1.16
1.22
1.84
1.1
0.6
Med
ian
10.
5021
2169
138
0.0
-0.3
01.
321.
321.
841.
10.
7
Mod
e1
0.50
11
491
10.
0-0
.30
0.00
0.00
1.69
0.8
0.5
S.D
161.
8622
5660
2510
0.5
0.40
0.57
0.44
0.19
0.5
0.5
Q1
10.
5010
1454
61
0.0
-0.3
01.
001.
151.
730.
80.
0
Q3
20.
5035
2888
289
0.3
-0.3
01.
551.
451.
951.
41.
0
95th
perc
entil
e23
5.00
7054
133
6518
1.4
-0.3
01.
851.
732.
121.
81.
3
Skew
ness
103.
001
1913
37
1.8
0.70
1.00
1.18
0.48
0.5
-0.1
Kur
tosi
s15
410
.00
342
024
820
932.
43.
800.
032.
534.
750.
1-1
.3
N58
558
558
558
558
558
558
558
558
558
558
558
558
558
5
BG1
51.
2625
2677
2110
2.0
0.90
1416
6913
4
Thre
shol
d 137
5.00
6913
819
771
3010
4.30
2222
7119
10
BG2
10.
5021
2169
138
0.0
0.90
2020
6813
5
Thre
shol
d 233
3.72
6513
318
963
286.
04.
3028
2672
198
C3.
21.
50.
92.
10.
825
.21.
02.
02.
800.
30.
20.
00.
30.
8
Ag,
Cu,
Pb,
Zn,
As a
nd S
b da
ta in
ppm
; da
ta f
or A
u in
ppb
, SD
– st
anda
rd d
evia
tion,
C–
coef
ficie
nt o
f va
riat
ion,
Q1
and
Q3–
fir
st a
nd t
hird
qua
rtile
s, N
– nu
mbe
r of
sam
ples
. M
ean:
Bac
kgro
und
(BG
1),
Thre
shol
d 1:
BG1
+ 2
sta
ndar
d de
viat
on.
Med
ian:
Bac
kgro
und
(BG
2),
Thre
shol
d 2:
BG2
+ 2
sta
ndar
d de
viat
ion.
Det
ectio
n lim
its:
Au:
1 pp
b, A
g: 0
.5 p
pm,
Cu:
1 pp
m,
Pb:
1ppm
, Zn
:
1ppm
, As
: 1
ppm
, Sb
: 1p
pm
H. YILMAZ
45
Figure 5. Stream sediment geochemistry of Au, Cu, Pb, Zn, As, Sb at the AYALE area.
STREAM SEDIMENT GEOCHEMICAL EXPLORATION FOR GOLD
46
Tabl
e 3.
St
atis
tical
val
ues
for
the
rock
chip
geo
chem
ical
dat
a se
t of
the
AYA
LE a
rea.
Elem
ents
AuAg
CuPb
ZnAs
SbM
oW
BiTl
AuAg
CuPb
ZnAs
SbM
oW
BiTl
Dat
aR
awLo
g10-
trra
nsfo
rmed
Min
imum
<1
<0,
5<
1<
1<
1<
1<
1<
1<
1<
1<
10.
00-0
.30
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
Max
imum
5400
130.
0023
000
5700
046
000
1120
027
918
737
303
293.
732.
104.
364.
764.
664.
053.
451.
663.
422.
481.
46
Mea
n31
57.
0039
786
373
732
550
214
165
1.19
0.06
1.6
1.18
1.47
1.87
0.9
0.25
0.37
0.55
0.46
Med
ian
120.
5020
1121
808
11
11
1.08
-0.3
01.
301.
041.
321.
900.
900.
000.
000.
000.
00
Mod
e1
0.50
171
11
11
11
10.
00-0
.30
1.23
0.06
1.04
0.00
0.00
0.00
0.00
0.00
0.00
S.D
754
18.0
019
2757
8950
2988
825
82
8139
61.
190.
670.
720.
910.
710.
800.
760.
400.
640.
600.
41
Q1
10.
5013
612
231
11
11
0.00
-0.3
01.
110.
741.
081.
360.
001.
000.
000.
000.
00
Q3
115
1.00
3940
4428
525
45
113
2.06
0.01
1.60
1.60
1.65
2.45
1.39
0.55
0.69
1.03
0.42
95th
perc
entil
e19
1539
.00
1608
482
1076
1834
124
832
3014
3.28
1.59
3.21
2.68
3.03
3.26
2.09
0.90
1.51
1.47
1.13
Skew
ness
34.
008
88
910
58
72
0.50
1.63
1.64
1.19
1.97
-0.2
20.
461.
432.
321.
011.
40
Kur
tosi
s14
17.0
084
6662
9610
627
6955
18-1
.40
1.23
3.74
2.63
6.12
-0.0
8-0
.31
1.26
6.48
0.02
0.68
N24
024
024
024
024
024
024
024
024
024
024
024
024
024
024
024
024
024
024
024
024
024
0
BG1
315
7.00
397
863
737
325
502
1416
516
.00.
061.
601.
181.
471.
870.
890.
250.
370.
550.
46
Thre
shol
d 118
2343
.00
4251
1244
110
792
2101
566
617
694
1748
.011
.00
53.0
32.0
41.0
91.0
20.0
8.0
13.0
11.0
9.0
BG2
120.
5020
1121
808
11
11
12.0
0.0
20.0
11.0
21.0
80.0
8.0
1.0
1.0
1.0
1.0
Thre
shol
d 215
2037
.00
3874
1158
910
079
1856
596
516
379
1344
.010
.030
.032
.041
.091
.020
.07.
011
.09.
07.
0
C2.
42.
605
77
35
15.
72.
41
1.0
4.5
0.2
0.2
0.2
0.0
0.9
1.5
1.5
1.0
1.0
Ag,
Cu,
Pb,
Zn,
As,
Sb,
Mo,
Cd,
W,
Bi a
nd S
dat
a in
ppm
; da
ta f
or A
u in
ppb
. SD
– st
anda
rd d
evia
tion,
C–
coef
ficie
nt o
f va
riat
ion,
Q1
and
Q3:
fir
st a
nd t
hird
qua
rtile
sN
– nu
mbe
r of
sam
ples
. M
ean–
bac
kgro
und
(BG
1),
Thre
shol
d 1–
BG1
+ 2
sta
ndar
d
devi
atio
n. M
edia
n: b
ackg
roun
d (B
G1)
, Th
resh
old1
: BG
1+ 2
sta
ndar
d de
viat
ion.
Det
ectio
n lim
its:
Au:
1 pp
b, A
g: 0
,5 p
pm,
Cu.
1ppm
, Pb
: 1
ppm
Zn:
1 p
pm,
As:
1ppm
, Sb
: 1
ppm
, M
o: 1
ppm
, W
: 1p
pm,
Bi:
1ppm
.
H. YILMAZ
47
Figure 6. Rock chip geochemistry of Au, Ag, Cu, As and Sb at the Tuztafl› area.
STREAM SEDIMENT GEOCHEMICAL EXPLORATION FOR GOLD
48
Tabl
e 4.
Stat
istic
al v
alue
s fo
r th
e 18
0-µm
soi
l geo
chem
ical
dat
a se
t of
the
AYA
LE a
rea.
Elem
ents
AuAg
CuPb
ZnAs
SbM
oW
BiS
AuAg
CuPb
ZnAs
SbM
oW
BiS
Dat
aR
awLo
g10-
trra
nsfo
rmed
Min
imum
<1
<0,
5<
1<
1<
1<
1<
1<
1<
1<
117
0.00
-0.3
00.
000.
001.
040.
000.
000.
000.
000.
001.
20
Max
imum
2100
2043
594
941
852
120
2910
3413
1617
3.32
1.31
2.64
2.98
2.62
2.72
3.31
1.01
1.53
1.11
3.21
Mea
n42
0.60
5021
9427
203
32
188
0.62
-0.2
91.
621.
151.
921.
130.
940.
390.
210.
142.
21
Med
ian
10.
5041
1783
1511
21
116
00.
00-0
.30
1.61
1.22
1.92
1.18
1.04
0.37
0.00
0.00
2.20
Mod
e1
0.50
371
701
11
11
172
0.00
-0.3
01.
560.
002.
070.
000.
000.
000.
000.
000.
00
S.D
166
1.00
4044
4744
108
0.4
41
133
0.82
0.12
0.26
0.38
0.21
0.54
0.47
0.37
0.37
0.30
0.23
Q1
10.
5030
1065
95
11
111
40.
00-0
.03
1.48
0.99
1.81
0.93
1.00
0.00
0.00
0.00
2.06
Q3
160.
5058
2411
625
186
21
223
1.20
-0.3
01.
761.
372.
061.
392.
390.
770.
380.
002.
35
95th
perc
entil
e17
80.
5010
341
184
104
298
107
369
2.25
-0.3
02.
011.
612.
262.
021.
470.
891.
000.
842.
57
Skew
ness
815
518
25
170.
53.
22.
44.
51.
0911
.50
-0.2
2-0
.85
-0.1
4-0
.58
-0.2
20.
131.
461.
760.
38
Kur
tosi
s75
234.
0035
380
7.2
4328
5-1
.215
5.3
330.
1413
74.
002.
730.
721.
201.
75-1
.77
0.70
1.42
1.62
N53
353
353
353
353
353
353
353
353
353
353
353
353
353
353
353
353
353
353
353
353
353
3
BG1
420.
6050
2194
2720
33
218
84.
00.
043
.015
.082
.012
.09.
03.
01.
01.
416
5.0
Thre
hold
137
42.
6013
010
918
811
523
63.
811
445
416
.00.
045
.021
.084
.018
.015
.09.
07.
05.
416
7.0
BG2
10.
5041
1783
1511
21
116
01.
000.
543
.017
.083
.016
.09.
02.
01.
01.
016
5.0
Thre
shol
d 233
72.
5012
110
517
710
322
72.
89
342
613
.02.
045
.023
.085
.022
.017
.08.
07.
05.
02.
7
C3.
91.
700.
82.
10.
51.
65.
40.
11.
30.
50.
71.
500.
000.
000.
200.
000.
300.
201.
001.
502.
000.
00
Ag,
Cu,
Pb,
Zn,
As,
Sb,
Mo,
Cd,
W,
Bi a
nd S
dat
a in
ppm
; da
ta f
or A
u in
ppb
. SD
– st
anda
rd d
evia
tion,
C–
coef
ficie
nt o
f va
riat
ion,
Q1
and
Q3:
fir
st a
nd t
hird
qua
rtile
s. N
– nu
mbe
r of
sam
ples
.M
ean–
bac
kgro
und
(BG
1),
Thre
shol
d 1–
BG1
+ 2
sta
ndar
d de
via-
tion.
Med
ian–
bac
kgro
und
(BG
2),
Thre
shol
d 1–
BG2
+ 2
sta
ndar
d de
viat
ion.
Det
ectio
n lim
its:
Au:
1 pp
b, A
g: 0
,5 p
pm,
Cu.
1ppm
, Pb
: 1
ppm
Zn:
1 p
pm,
As:
1ppm
, Sb
: 1
ppm
, M
o: 1
ppm
, W
: 1p
pm,
Bi:
1ppm
.
H. YILMAZ
49
1010
010
00
110100
200
Zn
Cu
(a)
R=
21
n=58
5
100
600
110100
1000
Zn
Pb
(e)
R=
0.8
n=53
3
1010
010
00
110100
1000
Zn
Pb
(b)
R=
0.3
2
n=58
5
110
100
700
110100
1000
4000
As
Au
(c)
R=
0.4
0
n=53
3
1010
080
0
110100
800
Zn
Cu
(d)
R=
0.5
n=53
3
Zn
110
100
1000
1000
070
000
110100
1000
1000
0
5000
0
Cu
(f)
R=
0.4
5
n=24
0
110
100
1000
1000
070
000
110100
1000
1000
0
8000
0
Zn
Pb
(g)
R=
1.0
n=24
0
110
100
1000
3000
0
110100
1000
8000
As
Au
(h)
R=
0.2
5
n=24
0
110
100
200
110100
1000
8000
Ag
Au
(i)
R=
0.2
8
n=24
0
Figu
re 7
.Lo
g-Lo
g co
ncen
trat
ions
of:
(a)
Cu v
ersu
s Zn
and
(b)
Pb v
ersu
s Zn
in 1
80-µ
m s
trea
m s
edim
ent;
(c)
Au v
ersu
s As
, (d)
Cu v
ersu
s Zn
and
(e)
Pb v
ersu
sZn
in 1
80-µ
m s
oil;
(f)
Cu v
ersu
s Zn
, (g
)Pb
ver
sus
Zn,
(h)
Au v
ersu
s As
and
(i)
Au v
ersu
s Ag
in r
ock
chip
at
the
AYAL
E ar
ea.
Discussion of Results
Arsenic exhibits a nearly universal enrichment in mosttypes of hypogene gold deposits (Boyle 1979). Gold-bearing polymetallic deposits and certain skarns areinvariably enriched in arsenic, as are the typical quartzveins at Fortitude Mine in Nevada, USA. In these types ofdeposit the arsenic content ranges from a few tens ofparts per million to percentage amounts in the ore.Because the gold is so intimately associated witharsenopyrite- and arsenic-bearing sulfosalts in somedeposits the element appears to be a lattice constituent ofthese minerals. The disseminated gold deposits of northcentral Nevada are all enriched in arsenic (Berger &Bethke 1984). However, the element is not only bound inAs minerals and As-bearing pyrite, which are commonlyassociated with Au mineralization (Yang & Blum 1999),but also forms widespread geochemical haloes around Audeposits, so that the element is commonly used as apathfinder in noble metal exploration. In thenorthwestern part of Hunan Province (China) manyAu–Sb (or Au–W) deposits occur in low-grademetamorphic rocks of Neoproterozoic age. Here,arsenopyrite is the only As-bearing mineral, occurring inminor quantities. Arsenic concentrations in these slatebelt deposits range from 0.10 to 2.36 wt% (mainlybetween 0.4 and 1.0%). However, As has never beenconsidered as pathfinder for Au-exploration in the earlierwork (Yang & Blum 1999). A similar geochemicalsignature to that of northwestern Hunan is recognized inlow-grade metamorphic rocks of western Turkey (Y›lmaz2003). Mesothermal gold mineralization closelyassociated with As is widespread in Upper Mesozoicmetagreywackes deposited in a collisional setting in theSouthern Alps of New Zealand (Craw 2001). Arsenic ispresent in solid solution in many of the sulfides, and inaccessory As minerals in mesothermal deposits (Craw2001). It is readily mobilized from these deposits atneutral to alkaline pH. In contrast to As behavior, Cu, Pb,Zn and Cd are dissolved and passed into soil under highlyacidic conditions. Arsenic is most stable in an oxidizingenvironment, being a constituent of basic sulfatearsenates. Oxidation of native As, arsenopyrite andvarious other arsenides and sulfarsenides yields a varietyof supergene arsenates and basic arsenate-sulfates, themost common being scorodite, Fe (AsO4).H2O, and Co-,Ni-, Pb-, Zn-, and Cu-arsenates (Boyle 1979). Of these,the most important in gold deposits is scorodite; the
others occur only where there are high contents of Ni,Co, Cu, Pb or Zn. All these minerals, in particularscorodite, tend to concentrate gold (Boyle 1979).Oxidation of primary As minerals yield arsenic acidH3AsO4. In these forms, arsenic is relatively mobile, andunder certain conditions considerable amounts of theelement may be removed from the deposits duringoxidation.
Under oxidizing conditions, and in the presence ofiron, inorganic arsenic species are predominantly retainedin the solid phase through interaction with iron oxy-hydroxide coatings on soil particles (Bose & Sharma2002). These authors described several types ofinteractions, i.e., adsorption on amorphous ironhydroxide and adsorption on ferrihydrite and co-precipitation of arsenic (III) and arsenic (V) with iron oxy-hydroxide occurring in an oxidizing environment.
No linear correlation occurs between Au and Ag, As,Sb, Cu, Pb, Zn in BLEG and 180-µm stream sedimentgeochemical and rock chip data (Table 5a & b; Figure 7)from the AYALE area. The critical value for t with 238degrees of freedom and 10% level of significance is t=1.645. Because most of the test statistics fall into uppercritical region, it is concluded that there are truecorrelations (r> 0.1) between the element variablesparticularly in the rock chip (Table 5b) data set (Davis1986). Nevertheless, weak correlations occur betweenCu-Zn and Pb-Zn in 180-µm (Figure 7). All these may becaused by different dissolution and transportcharacteristics of these metals in secondary environmentas well as their emplacement into the host rock atdifferent levels and phases (Boyle 1979; Craw 2001;Bose & Sharma 2002). On the other hand, very weakcorrelations between Au and Ag and As in rocks (Table 5a& b; Figure 7), as in 180-µm stream-sediment samples,at AYALE suggests that they may be related to differentmineralizing events, thereby indicating possibleintroduction of Au, Ag and As in three different phases ofmineralization within the same structural zone. Althoughnot always, anomalous gold zones are usuallyaccompanied by anomalous As zones (Figure 5).Relatively higher correlations occurring between Cu andPb, Zn; Pb and W; Zn and Sb, W and, Mo and W (Table5a & b; Figure 6) in the same mineralized rock-chipsamples may also indicate two distinct phases ofmineralization at least two different times because theseelements would be expected to be found associated within
STREAM SEDIMENT GEOCHEMICAL EXPLORATION FOR GOLD
50
intrusive-centred porphyry or skarn systems. Thepresence of weak to moderate correlations between Cuand Pb, Zn as well as W and Pb, Zn, Sb, Mo in rock-chipsamples may suggest that 180-µm stream-sedimentsamples should also be analyzed for Mo and W duringfurther exploration in the AYALE area. Elementscommonly found enriched in mesothermal lode golddeposits in metamorphic terrains include Au, Ag, As, Sb,Hg, W, Bi and Mo (Pirajno 1992). Less commonly, Pb, Znand Cu may be present. Therefore, the AYALE area, morespecifically the Tuztafl› area, may be a significant targetfor some of the above-mentioned mineralization hostedby metamorphic rocks.
Much of the arsenic in the Tuztafl› area might havebeen co-precipitated and/or adsorbed by hydrous iron andother oxides or have reacted with cations such as Fe andCu to give a variety of insoluble arsenates during varioushydrolytic and colloidal reactions in oxidized zones assuggested by Boyle (1979), Craw (2001) and Bose &Sharma (2002) elsewhere. These reactions take placemainly between pH from 4 to 7 (Bose & Sharma 2002),and this may also be so in the Tuztafl› area where someof the illite and chlorite formed possibly by weathering
indicate weakly acidic to neutral conditions. The wallrocks and gangue also contain abundant carbonateminerals such as calcite to neutralize the downwardmoving solutions. Arsenic concentration is variable andclearly not exclusively related to Au enrichment except fortheir coexistence within the same structure (Table 6a & b;Figures 5–7). A similar situation exists for the silver aswell. Positive correlation coefficients between Au and Agand, Au and As, are weak to moderate (r< 0.5) inthe180-µm in soil data set. The critical value for t with531 (samples) degrees of freedom and 10% level ofsignificance is t= 1.645. It is concluded that there aretrue correlations (r > 0.1) between the significantnumbers of element variables within the soil (Table 6b)data set (Davis 1986). These metal associations can onlybe encountered in epithermal and to a certain extent inmesothermal precious metal deposits. A close associationof Au with As and Ag in soil as well as a very closeassociation of W with Sb, Pb, Zn and Mo in rock chipsamples indicate two distinct geochemical signatures thatare possibly related to the epi- to meso-thermal preciousand base metal skarn mineralization systems in theAYALE area.
H. YILMAZ
51
Table 5. Matrix of correlations between measured variables for Tuztafl› prospect rock chip data set (a) and calculation of t values (b) using thecorresponding correlation coefficiecients in (a).
Var* Au Ag Cu Pb Zn As Sb Mo W Bi
Tl -0.09 0.05 0.36 0.06 0.07 -0.01 -0.02 0.12 0.01 0.22Bi 0.21 0.01 0.20 0.07 0.05 0.07 -0.01 0.05 0.02W -0.04 0.22 0.37 0.97 0.96 0.18 0.61 0.39Mo 0.01 0.33 0.18 0.32 0.34 0.05 0.56Sb -0.02 0.11 0.29 0.57 0.60 0.31As 0.25 0.13 0.07 0.19 0.18 (a)Zn -0.04 0.27 0.45 1.00Pb -0.04 0.27 0.44Cu 0.05 0.18Ag 0.28
Var** Au Ag Cu Pb Zn As Sb Mo W Bi
Tl -1.39 0.77 5.95 0.93 1.08 -0.15 -0.31 1.86 0.15 3.48Bi 3.31 0.15 3.15 1.08 0.77 1.08 -0.15 0.77 0.31W -0.62 3.48 6.14 61.56 52.89 2.82 11.88 6.53Mo 0.15 5.39 2.82 5.21 5.58 0.77 10.43Sb -0.31 1.71 4.67 10.70 11.57 5.03As 3.98 2.02 1.08 2.99 2.82 (b)Zn -0.62 4.33 7.77 1090.79Pb -0.62 4.33 7.56Cu 0.77 2.82Ag 4.50
Var* - variable; high-lighted values refer to relatively higher correlations between elements, n= 238.Var** - variable; critical value t= 1,645 for 238 samples. High-lighted values suggest that there is a real correlation between variables.
Although the Akp›nar-Evciler south area stretchingfrom Tuztafl› to Karaköy hosts gold-Ag-As-rich quartzveins/breccia zones, a major, coherent 180-µm streamsediment As anomaly appears to be confined to astructural divide, where Upper Cretaceous–Palaeocenemélange, Upper Oligocene granitoids and Miocenevolcanic rocks, overlie the exposed metamorphic core.This may be caused by the erosion of possible As-bearinghigh-level mineralization zones during exhumation of themetamorphic rocks from ~14-km to ~7-km along anorthward-dipping ductile shear zone (Figures 1, 2 & 5;Okay et al. 1991; Okay & Sat›r 2000).
BLEG, 180-µm stream-sediment and soil samplingtechniques appear to be an effective reconnaissance toolin the AYALE area in west Turkey. The persistence of180-µm Au anomalies for less than 1000 m downstreamfrom the Tuztafl› Prospect (from 90 ppb to 7 ppb)suggests that 180-µm stream-sediment sampling is notas efficient as BLEG on 212 ppb) anomalies.
At the initial stage of regional reconnaissance, BLEGanomalies indicated that Ag in the Tuztafl› area mightoccur as electrum or sulfosalts (log-transformed Ag/Au:4.6). This was further supported by high Ag contents(130 ppm) and log-transformed Ag/Au ratios (3).Arsenic-Sb and Ag are the most reliable pathfinderelements for Au in the study area.
Conclusions
BLEG stream sediment geochemical sampling is a time-and cost-efficient method in assessing large areas ofrugged terrains (1350 km2 in this case). The re-discovery
STREAM SEDIMENT GEOCHEMICAL EXPLORATION FOR GOLD
52
Table 6. Matrix of correlations between measured variables for Tuztafl› prospect soil data set (a) and calculation of t values (b) using thecorresponding correlation coefficiecients in (a).
Var* Au Ag Cu Pb Zn As Sb Mo W Bi
S 0.00 0.05 0.23 0.08 0.44 0.24 -0.04 -0.36 -0.07 -0.20Bi 0.15 -0.03 0.07 -0.03 -0.04 -0.01 -0.01 0.45 0.04W 0.01 -0.04 0.05 0.01 0.06 -0.08 0.05 -0.02Mo 0.15 0.09 0.06 -0.03 -0.13 -0.10 0.13Sb 0.03 0.01 0.02 -0.02 -0.03 -0.01As 0.40 0.11 0.08 0.08 0.07 (a)Zn -0.02 0.01 0.51 0.18Pb 0.05 0.02 0.05Cu 0.08 0.02Ag 0.43
Var** Au Ag Cu Pb Zn As Sb Mo W Bi
S 0.00 1.15 5.44 1.85 11.27 5.69 -0.92 -8.88 -1.61 -4.69Bi 3.49 -0.69 1.61 -0.69 -0.92 -0.23 -0.23 11.59 0.92W 0.23 -0.92 1.15 0.23 1.38 -1.85 1.15 -0.46Mo 3.49 2.08 1.38 -0.69 -3.02 -2.31 3.02Sb 0.69 0.23 0.46 -0.46 -0.69 -0.23As 10.04 2.55 1.85 1.85 1.61 (b)Zn -0.46 0.23 13.64 4.21Pb 1.15 0.46 1.15Cu 1.85 0.46Ag 10.95
Var* - variable; high-lighted value refer to relatively higher correlations between elements, n= 531.Var** - variable; Critical value t= 1,645 for 531 samples. High-lighted values suggest that there is a real correlation between vaiables.
H. YILMAZ
53
XL-1
XL-3
XL-5
XL-9
XL-11
XL-13
XL-15
XL-17
F
F
F
200
50
100
100
F
0-25
25-100100-400400-1600>1600
Au (ppb)quartz veins
road
0 200m
drainage
470
000
43 94 000
XL-1
XL-3
XL-7
XL-9
XL-11
XL-1
3
XL-1
5
XL-1
7
0-25
25-100
100-400
>400
0 200 m
As (ppm)
470
000
43 94 000
XL-7
XL-5
(a)
(b)
Figure 8. Distribution of (a) Au and (b) As in 180-µm soil at the Tuztafl› Prospect.
of the Tuztafl› prospect during the follow up of an alreadydelineated BLEG anomaly is an exploration success using180-µm stream sediment and soil geochemistry.Moreover, the BLEG sampling technique proved to be avery sensitive exploration tool even in discovering small-scale mineralization in areas with well-developed drainageas in the Tuztafl› area. Identification and sampling ofaltered and mineralized rock float in streams was criticalin ranking the regional geochemical results. Soil samplingeffectively delineated Au and As geochemical zonings. TheBLEG geochemical technique should not be used inisolation and should be accompanied by a compilationstudy of recent, old and ancient workings, and knownmineralization since the Tuztafl› deposit had been minedon a small-scale mine during ancient times. Two distinct
180-µm Au and As geochemical signatures in the Tuztafl›area appear to be confined to medium- to high-grademetamorphic rocks forming the footwall and crustalhanging-wall accretionary mélange of a majordetachment fault, respectively.
Acknowledgement
I would like to express my appreciation to EurogoldMadencilik/Normandy Mining Ltd., Turkey for generousfinancial support to the project during my tenure asEurogold Exploration Manager. Reviewers Robert B.Cook and anonymous are thanked for their invaluablecomments in improving the quality of this paper. John A.Winchester helped with English of the final text.
STREAM SEDIMENT GEOCHEMICAL EXPLORATION FOR GOLD
54
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Received 03 August 2005; revised typescript received 29 June 2006; accepted 13 October 2006