SEM and Gold deportment study - Geology/GIS …geomantiacogs.com/wp-content/uploads/2015/04/ER_SEM...Sediment‐hosted gold mineralization was recently discovered on Erika property,

ERIKA Project

Guerrero State, Mexico

SEM and Gold deportment study

Prepared for:

Tarsis Resources Ltd

1103-750 W Pender St

Vancouver, BC

Canada, V6C 2T8

Tel: +1 (604) 689 7644

Fax: +1 (604) 689 7645

By:

Venessa Bennett (Ph.D)

Consulting Geologist

33 Roundel Rd

Whitehorse, YT

Canada, Y1A 3H4

Tel: +1 (867) 335 5245

Email: [email protected]

Key Point Summary

Polished thin sections were prepared for 6 samples from the 2011 drill program completed on the

Erika project of Tarsis Resources Ltd. Standard binocular and petrographic microscopy was carried out

on these polished thin sections and subsequently prepared for Scanning electron microscopy (SEM)

modal mapping and mineral analysis.

SEM mineral mapping completed on 6 polished thin sections from Au mineralized samples

demonstrates the presence of several ore fluid processes that are analogous to Carlin‐style

mineralization including decalcification, decarbonatization, argillization and associated silicification of

calcareous siltstone.

Decalcification (removal of Ca) and formation of dolomite occurs in samples more distal to higher

grade Au mineralization. Samples more proximal are devoid of dolomite. Decarbonatization (complete

removal of carbonate) is associated with the influx of illite, quartz and pyrite.

Pyrite grains within zones of intense decarbonatization are distinct in the occurrence of 'fuzzy'

arsenian rich pyrite growth either as fine‐grained disseminated grains or as thin micron scale rims on

different generations of pre‐existing pyrite. Arsenian rich pyrite is interpreted to be associated with Au

mineralization.

Arsenic rich clay is associated with the growth of arseniosiderite in samples that are devoid of

arsenic sulphides and pyrite. Micron scale native gold is observed within arseniosiderite grains and

disseminated within the matrix of As rich clay.

Pathfinder elements, As‐Hg‐Sb‐Tl are either highy anomalous or show moderate to strong

correlation within gold. The elements were observed to have mineral hosts of orpiment, realgar, As‐clay,

arseniosiderite and arsenian pyrite, cinnabar and stibnite, respectively. The mineral host for Tl was not

observed.

Two types of structures were observed to be associated with sediment hosted Au‐mineralization at

Erika including, (ii) high‐angle brittle, normal and dilational faults and calcite vein faults that occur within

the peripheral calcite vein halo and (ii) bedding parallel to subparallel shear zones that postdate high

angle structures and locally preserve reidel shear geometries.

Collectively, the macro and microscale datasets available for the Erika property support the

interpretation of a sediment‐hosted gold target (Carlin‐style) as opposed to a high‐sulphidation

epithermal target.

Geomantia Consulting

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1.0 Introduction

Sediment‐hosted gold mineralization was recently discovered on Erika property, Guerrero state,

Mexico, 2011 (Fig. 1) by Tarsis Resources Ltd. Previous exploration programs, that included geological

mapping, soil and silt geochemical sampling and an 8‐hole drill program, were conducted by Almaden

Minerals and focussed on delineation of high sulphidation Au‐Ag epithermal mineralization. The Coacoyula

area, which is known for historical epithermal mercury deposits, also exhibits intense clay alteration

consisting of kaolinite‐alunite‐dickite‐svanbergite‐gypsum associated with opaline and massive silicification,

and local dolomitization of limestone host rocks (Fonseca, 2007). Drill results yielded no significant high

sulphidation Au‐Ag mineralization, however, one of the 8 drill holes (97‐EK‐03) intersected 1,078 ppb Au,

immediately above a fault intersection.

In 2010, Tarsis Resources Ltd initiated a drill program to test the source of a central As‐Hg‐Sb soil

geochemical anomaly (Drill Transect 1). Eight drill holes were completed along an E‐W transect, immediately

south of the town of Coacoyula. Despite intense clay, Hg and iron oxide mineralization in the host limestone,

no significant gold mineralization was intersected. After review of both the 1997 and 2010 drill core, a

second E‐W drill transect was designed to assess potential extension of Au mineralization that had been

intersected in DDH 97‐EK‐03. Au mineralization was intersected in 4 of 5 holes, with best interval 1.14g/t

over 10.28m.

Mineralization encountered did not share characteristics of typical high‐sulphidation epithermal

targets, but rather exhibited many features consistent with sediment‐hosted gold mineralization. In order to

verify the style of alteration and mineralization intersected in the 2011, transect B drill program, a suite of

samples were collected from several mineralized intervals to complete petrographic and Scanning Electron

Microscope (SEM) studies. The core objectives of the study included:

(1) Documentation of the location and intensity of decarbonatization within the mineralized

intervals and assessment of the relationship to gold mineralization.

(2) Assessment of which minerals hosted key pathfinder elements As‐Hg‐Tl‐Sb within the

mineralized intervals sampled.

(3) A Au deportment study to define the mode of gold occurrence within the mineralized intervals.

The main purpose of this work was to assess the veracity of the application of a sediment‐hosted

gold deposit model and more specifically, a Carlin‐style deposit model. If this could be verified, then any


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future exploration programs would require modification to successfully delineate this style of mineralization

which manifests in entirely different modes than high‐sulphidation epithermal deposits.

A suite of 6 samples were selected for polished thin section preparation from diamond drill holes

11‐ER‐09, 11‐ER‐14 and 11‐ER‐15. A standard petrographic and binocular microscopy review was completed

on these samples, which were subsequently prepared for analysis on the scanning electron microscopy

(SEM). All six samples were mapped using Mineral Liberation Analysis software on the Scanning Electron

Microscope (MLA‐SEM) at Memorial University of Newfoundland.

2.0 Geological Setting

The Erika Property lies on Guerrero‐Morelos Platform, which consists of a thickness of over 2,000 m

of Mesozoic carbonate rocks unconformably overlaying Early Cretaceous to Late Jurassic island arc

sequences of Guerrero Terrane. Guerrero‐Morelos Platform is bound to the south by the Xolapa

metamorphic core complex, and to the north it is covered by Trans Mexican Volcanic Belt magmatic rocks

(Figure 2; Fonseca, 2007). The sedimentary rocks of Guerrero‐Morelos Platform were folded during Late

Cretaceous to Early Tertiary Laramide deformation. Guerrero‐Morelos Platform has three units: Morelos

Formation (Albian to Cenomanian limestones and dolostones; Cuautla Formation (Turonian calcareous

shales and limestones); and Mezcala Formation (Coniancian to Campanian, calcareous shales with

interbeded sandstones; Fonseca, 2007).

The Coacoyula epithermal district lies at the northern flanks of the Sierra Madre del Sur

physiographic and geologic provinces, where Tertiary plutonic rocks of adakitic composition occur

associated with large gold‐skarn deposits approximately 15 kilometres south of Erika (Fonseca, 2007).

Lithologies underlying the Erika Property include a Cretaceous sedimentary sequence that includes the

Morelos Formation limestone and overlying calcareous siltstone and mudstone of the Mezcala Formation.

The Mesozoic sedimentary sequence is partially covered by Tertiary felsic volcanic flows, breccias and

volcaniclastic accumulations (Fig. 3).

The Mesozoic sedimentary package strikes generally to the north, and is overlain by a thin package

of Tertiary felsic volcanic rocks. The felsic volcanic unit consists of brecciated volcaniclastics containing fine‐

grained, angular to sub‐rounded lithic fragments, quartz phenocrysts, rare pumice fragments. The property

includes several areas of intense clay alteration, from which clay has been mined for industrial applications

(Fonseca, 2007). A compilation of interpreted lineaments, faults, and dikes from air photos of Erika Property


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by Leach and Corbett (1996; Fig. 3) demonstrates that important structural trends are north‐northwest and

northeast. The property is located along a major north‐ to north‐northwest trending structural zone that

extends over 45 km north to the Taxco silver veins deposit, and 15‐20 km south to the Au‐skarn deposits of

Mezcala district (Fonseca, 2007).

3.0 Alteration/Mineralization and Au Pathfinders

Alteration associated with gold mineralization occurring at the Erika property includes:

1. Peripheral calcite veining that formed in response to early‐stage decalcification of host calcareous

sedimentary rocks (Fig. 4a,b).

2. Calcite + orpiment and/or realgar veining associated with low grade (<0.1g/t) Au mineralization

(Fig. 4c).

3. Disseminated orpiment mineralization associated with zones of decalcification (Fig. 4d).

4. Partial to complete decarbonatization (removal of carbonate) associated with disseminated

arsenic sulphides, pyrite and gold mineralization (Fig. 4e‐g).

Gold mineralization is associated with zones of intense decarbonatization, increased SiO2 and

anomalous Tl‐Hg‐As‐Sb. Dissolution collapse breccias occur in both intensely decarbonatized calcareous

siltstone (Mescala Formation; Fig. 4h) and limestone (Morelos Limestone; Fig. 4j). Additionally, a distinct

yellow‐green clay phase hosts mineralization (Fig. 4i).

4.0 MLA‐SEM Modal Mapping

Six polished thin sections were selected for scanning electron microscopy analysis using the FEITM

Quanta 650 field emission Scanning Electron Microscope (SEM). Samples chosen for the analysis are listed

with associated assay data in Table 1 and illustrated in Figure 5.

The purpose of the SEM study was to utilize the automated Mineral Liberation Analysis (MLA)

software to map the mineralogy of each polished surface. The data generated were subsequently used to

calculate mineral modes (wt %) and characterize the mineral associations present. The end goal of this

mapping process was to establish generalized ore and alteration mineral relationships and to use the semi‐


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Sample FROM TO Au_ppm Ag_ppm As_ppm Hg_ppm Sb_ppm Tl_ppm Mo_ppm Ba_ppm Se_ppm Te_ppm W_ppm S_% Fe_% Ca_% Cu_ppm Pb_ppm Zn_ppm

ER‐11‐09_306.66‐307.05m 306.66 307.05 0.459 7.56 >10,000 20.4 616 78.6 58.1 80 12.2 0.33 0.61 4.27 2.46 4.62 18.4 10.4 76

ER‐11‐09_307.43‐307.58m 307.43 307.58 0.89 6.65 451 24.1 73.1 44.3 24.4 80 4.9 0.38 0.34 2.63 1.88 5.41 10.3 7.6 317

ER‐11‐14_274.50‐274.56m 274.29 274.83 2.07 0.79 9040 38.5 75 230 1.4 80 3.2 0.69 0.5 3.64 2.29 10.85 19.6 8.3 54

ER‐11‐14_274.90m 274.83 275.05 4.17 1.6 1200 56.8 9.3 40.4 1.27 50 2.5 0.77 0.33 2.67 1.81 12.95 15.1 6.6 15

ER‐11‐15_297.52‐297.58m 296.42 297.82 1.775 1.81 >10,000 25.4 3570 53.9 52.6 800 0.6 2.71 0.65 0.01 2.35 3.77 19.9 10.3 90

ER‐11‐15_298.03‐298.08m 297.82 299.1 0.53 3.72 >10,000 15.75 3070 510 206 70 56.6 1.39 0.28 6.88 0.84 19.15 8.4 3.8 36

Table 1: Geochemical assay data for samples presented in SEM study. Samples underwent partial digestion and may values for some elements may be an underestimate


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quantitative analytical capability of the SEM to determine which mineral phases hosted both Au and main

Au pathfinder elements.

Modal Mapping ‐ Methodology

Modal mapping using the automated MLA‐SEM technique involves collection of back‐scattered

electron and X‐ray spectra data across an entire offcut surface. The SEM sample‐stage is programmed to

systematically move the sample at equal increments in both the X and Y directions to allow collection of the

two datasets. For BSE data collection the entire range of mineral brightness values (i.e. mean atomic

number) is acquired. Data acquisition occurs in a series of mosaic images which are subsequently merged

together into one image of the polished surface (Figs. 6‐11).

Additionally, a uniformly spaced point grid is created across the entire thin section and at each point

location x‐ray spectra are collected. Each of these point x‐ray spectra are subsequently matched to a

reference x‐ray spectra mineral list created for the project. Any minerals that do not match the mineral

reference list are classified as unknown, which are reviewed and identified after the automated analysis is

complete (post‐processing). Once all mineral phases present are identified and assigned a representative X‐

ray spectra and mineral formula, a final colourized mineral map is produced (Fig 6‐11) and modal

abundances are calculated by both wt% (Table 2). In the case of the Erika sample suite, an X‐ray sampling

strategy was developed to overcome data point collection problems caused by the fine grained matrix that

occurs in all 6 samples. Rather than reduce the sampling distance between X ray points to a few microns, X‐

ray spectra for a sampling area (100x100microns) was collected and stored. Thus, a matrix X‐ray library was

generated that represented a composite X‐ray spectra of all minerals that occurred within the 100x100

micron averaging window. Five separate matrix types were identified:

i) Ca‐rich matrix: Quartz‐Albite‐Calcite and unidentified Ca‐rich clays

ii) Moderate abundance Ca‐matrix: Quartz‐Albite‐Calcite‐minor Ca‐clays

iii) Ca‐poor matrix A: Illite‐quartz‐pyrite

iv) Ca‐poor matrix B: Quartz‐illite‐pyrite (distinct from (iii) due to different proportions of minerals).

v) As‐rich clay: Quartz‐illite‐As rich clay.


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ER‐11‐09 ER‐11‐09 ER‐11‐14 ER‐11‐14 ER‐11‐15 ER‐11‐15

306.66‐307.05m 307.43‐307.58m 274.50‐274.56m 274.90m 297.52‐297.58m 298.03‐298.08m

Mineral Wt% Wt% Wt% Wt% Wt% Wt%

Apatite 0.05 0.19 0.06 0.06 0.07 0.09

Quartz 12.84 11.27 6.45 3.65 5.59 9.68

White‐mica 0.11 0.03 0.13 0.23 0 0.02

Illite 1.28 6.74 2.29 5.96 7.86 16.18

Ca Rich Matrix: Quartz‐Albite‐Calcite‐Ca Clay 5.55 13.52 21.96 24.66 5.76 3.06

Moderate Ca Matrix: Quartz‐Albite‐Calcite 23.5 11.48 11.57 6.36 11.05 8.22

Ca Poor Matrix‐A: Quartz‐Illite 42.13 26.85 21.78 16.61 18.22 31.69

Ca Poor Matrix‐B: Quartz‐Illite 2.69 5.11 3.02 6.55 8.57 5.29

As‐Rich Clay‐Quartz‐Illite Matrix 3.49 5.74 2.17 3.71 37.42 3.23

Rutile 0.02 0.03 0.01 0.01 0.01 0.01

Dolomite 3.04 12.32 0.04 0.01 0 0

Calcite 0.32 2.13 26.56 28.52 0.04 2.28

Sericite 0.13 0.12 0.13 0.14 0.09 0.09

Muscovite 0.03 0.01 0.02 0.01 0.01 0.01

As‐Ca_Fe siderite 0.03 0.05 0 0 0.71 0

Diagenetic_Kaolinite 0.05 0.01 0.19 0.37 0 0.01

Barite 0.02 0.1 0.01 0 0 0.02

Gypsum 0 0 0.19 0.03 0 16.63

Pyrite 0.86 1.32 0.91 1.4 0 1.13

Pyrite‐altrd 1.21 1.42 1.34 1.42 0 1.54

Orpiment‐Qtz_illite 0.11 0.07 0.26 0.08 0.01 0.22

Orpiment 1.89 0 0.69 0 0 0.43

Altd_Arseniosiderite 0.63 1.44 0.18 0.2 4.55 0.16

Total 100 100 100 100 100 100

Table 2: Modal calculations by weight %.


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Modal Mapping ‐ Results per sample

ER‐11‐09_306.66‐307.05m is a strongly decalcified and decarbonatized siltstone crosscut by several high

angle minor structures and several quartz veins. Both the minor faults and calcite veins terminate before a

horizon of intense decarbonatization associated with orpiment‐illite‐quartz‐pyrite growth (Fig. 6a‐d).

Dolomite locally replaces calcite adjacent to zones of decalcification (Fig. 6e). Total clay rich matrix material

comprises 77.4 wt% of the sample, with Ca‐rich matrix representing only 5.5wt%. Illite and quartz represent

1.28 and 12.8 wt%, respectively. Dolomite, which replaces calcite constitutes 3.04wt%, pyrite and altered

pyrite comprise approximately 2wt% and disseminated orpiment represents 1.9wt% of the mode. Accessory

phases include apatite, rutile, barite, kaolinite and sericite.

ER‐11‐09_307.43‐307.58m is a deformed tectonic breccia that is has undergone decalcification and less

intense decarbonatization (Fig. 7a‐d). Siltstone breccia clasts are strongly flattened and preserve evidence of

rotation. Coarse‐grained calcite formed in a low strain window adjacent to the largest siltstone clast present

in the slide. Dolomite replaces calcite throughout the slide. The deformed breccia matrix is more pervasively

decarbonatized than siltstone clasts (Fig. 7e). Total clay rich matrix material comprises 62.7 wt% of the

sample, with Ca‐rich matrix representing 13.5wt%. Illite and Quartz represent 6.74 and 11.3 wt%,

respectively, calcite and dolomite comprise 2.13 and 12.3wt%, respectively. Pyrite and altered pyrite

comprise approximately 2.7wt% and disseminated orpiment represents 1.9wt% of the mode. Accessory

phases include apatite, rutile, barite, kaolinite and sericite.

ER‐11‐14_274.50‐274.56m is a moderately deformed dissolution collapse breccia that has undergone

intense decarbonatization in the matrix enclosing the limestone and siltstone breccia clasts (Fig. 8a‐e).

Breccia clasts have undergone variable decalcification and locally contain coarse‐grained disseminated

orpiment. Total clay rich matrix material comprises 60.5 wt% of the sample, with Ca‐rich matrix

representing 21.96 wt%. Illite and quartz represent 2.29 and 6.45 wt%, respectively. Dolomite was not

recognized in this sample, whereas calcite comprised 26.56wt% of the estimated mode. Pyrite and altered

pyrite represent 2.25wt% and disseminated orpiment comprises 0.7wt%. Accessory phases include apatite,

rutile, gypsum, kaolinite and sericite.

ER‐11‐14_274.90m is a dissolution collapse breccia that is has undergone intense decarbonatization in the

matrix enclosing the limestone and siltstone breccia clasts (Fig. 9a‐e). Rounded breccia clasts have

undergone variable decalcification. Total clay rich matrix material comprises 57.9 wt% of the sample, with


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Ca‐rich matrix representing 26.66 wt%. Illite and quartz represent 5.59 and 3.65 wt%, respectively.

Dolomite was not recognized in this sample, whereas calcite comprised 28.52wt% of the estimated mode.

Pyrite and altered pyrite represent 2.82 wt% Accessory phases include apatite, rutile, gypsum, kaolinite and

sericite.

ER‐11‐15_297.52‐297.58m is a heterogeneous, compositionally banded clay rich sample. Banding is defined

by a late‐stage As rich clay that pervasively has infiltrated a quartz‐illite dominant clay (Fig. 10a‐e). The As‐

rich clay species within the sample is associated locally with a distinct As‐Fe mineral (arseniosiderite). Total

clay rich matrix material comprises 81.02 wt% of the sample, with Ca‐rich matrix representing 5.76 wt%.

Illite and quartz represent 7.86 and 5.59 wt%, respectively. Dolomite was not recognized and calcite was

only observed in trace abundances. Additionally, orpiment and pyrite were not identified. Arseniosiderite

comprised 4.55 wt%. Accessory phases include apatite and sericite.

ER‐11‐15_298.03‐298.08m is a variably decalcified and decarbonatized siltstone with coarse grained gypsum

laths that are intergrown with orpiment and spatially associated with concentrations of illite (Fig. 11a‐e).

Total clay rich matrix material comprises 51.49 wt% of the sample, with Ca‐rich matrix representing 3.06

wt%. Illite and quartz represent 16.18 and 9.68 wt%, respectively. Dolomite was not recognized in this

sample, whereas calcite comprised 2.28wt% of the estimated mode. Pyrite and altered pyrite represent

2.67wt% and disseminated orpiment comprises 0.4wt%. Accessory phases include apatite, rutile, barite,

kaolinite and sericite.

Mineral mapping of the Erika sample suite illustrates the occurrence of both decalcification and

decarbonatization in Au‐bearing rocks. Apart from the Au‐bearing clay sample, ER‐11‐15_297.52‐297.58m,

pyrite abundances range from 2 ‐ 2.8 wt% in all samples. Importantly, the occurrence of dolomite in

samples from ER‐11‐09 (and absence from ER‐11‐14 and 15) implies this drill hole intersected a more distal

component of the Au mineralizing system, which is consistent with the higher gold grades that were

intersected in holes ER‐11‐14 and 15 (i.e. more proximal).

5.0 Gold Deportment and Pathfinder Mineral Hosts

A examination of the sites of gold deposition was carried out on samples ER‐11‐14‐274.5‐274.56m

and ER‐11‐15‐297.52‐207.58m. Carlin‐style gold mineralization is typically associated with the occurrence of

submicron, invisible Au in trace element‐rich pyrite and marcasite. Gold‐bearing pyrite


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and marcasite occur as discrete grains, generally less than a few micrometers in diameter, or as arsenian rich

narrow rims on earlier formed pyrite grains (Cline et al., 2005). An important objective of SEM examination

of the Erika sample suite was to assess whether arsenian pyrite was present in samples that correlated with

elevated gold concentrations. Figure 12a presents the mineral map for sample ER‐11‐14‐274.5‐274.56m and

associated SEM images for various locations across the sample surface. Irregular, arsenian pyrite rims and

disseminated arsenian pyrite grains were identified within strongly decarbonatized material that formed a

breccia matrix enclosing dissolution collapse breccia clasts. A cursory review of pyrite grains in other

samples (Fig. 12b‐e), demonstrated the ubiquitous presence of 'fuzzy' arsenian rich pyrite rims on several

different pre‐existing pyrite generations. Framboidal pyrite, euhedral pyrite and inclusion‐rich pyrite grains

that occurred in decarbonatized zones were all associated with the growth of thin arsenian pyrite rims up to

5 microns wide.

Sample ER‐11‐15‐297.52‐207.58m is a heterogeneous dominantly clay‐bearing sample that is

associated with elevated Au values (up to 1.775g/t; Fig. 13a). No pyrite or arsenic sulphide minerals were

identified in this sample, however two distinct clay matrix types were mapped out including (i) an early

stage Ca‐poor quartz‐illite clay matrix, similar in composition to the clay matrix compositions comprising

strong zones of decarbonatization in the other samples examined in the study, and (ii) and a late stage As

rich clay phase that post‐dates the Ca‐poor clay matrix (Fig. 13c). A distinctive Ca‐Fe‐As oxide species,

arseniosiderite, is directly associated with the As rich clay matrix (Fig. 13b‐d). Micron size native gold was

identified within both arseniosiderite grains and disseminated with the As rich clay matrix, implying a second

gold bearing event post‐dating the decarbonatization and arsenian pyrite rim growth event. The two gold

events likely represent a continuum of one gold bearing fluid phase. The Au rich clay intervals appear to be

associated with infilling of voids (kharsts) below the siltstone/limestone contact, whereas the arsenian

pyrite gold bearing event is exclusively within decarbonatized siltstone.

Several pathfinder elements were identified to have a moderate to strong correlation with gold (Hg‐

Sb‐Tl or were extremely anomalous (As). Binocular and SEM observations identified:

1. Arsenic occurred as orpiment, realgar, As‐rich clay, As rich pyrite and arseniosiderite. In one

sample, orpiment was observed associated with gypsum, where gypsum laths grew at the expense

of orpiment. Alternatively, orpiment grains represented a nucleation point from which the gypsum

laths grew (Fig. 14a‐c).

2. Hg was locally observed to form as small grains of cinnabar at the outermost margins of pre‐

existing pyrite grains (Fig. 14d).


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3. Rare radiating stibnite grains were observed replacing a fine‐grain siltstone matrix (Fig. 14e)

The mineral host for Tl was not identified.

6.0 Structural Observations

Qualitative lineament analysis of the Erika property (Fig. 3) indicate that high‐angle NNW and NE

structural orientations prevail. On a regional scale, these structures represent part of an extensive north‐ to

north‐northwest trending structural zones that extends over 45 km north to the Taxco silver veins deposit,

and 15‐20 km south to the Au‐skarn deposits of Mezcala district (Fonseca, 2007). The nature and geometry

of fault structures controlling sediment‐hosted gold mineralization at Erika are currently not well

understood, but are tentatively correlated to N‐trending regional faults. Examination of drill core indicates

that two types of structures related to both alteration and mineralization are present, including:

1. High angle to core‐axis and bedding brittle faults and dilational calcite vein faults (Fig. 15). High

angle brittle faulting is typically associated with brecciation and focussed decarbonatization (Fig.

15c‐e). Kinematic observations indicate normal and dilatant displacement (Fig. 15a, b). Dilatant

calcite vein faultings is particularly well developed in the peripheral calcite vein halo (to Au

mineralization).

2. Bedding parallel to subparallel shear zone development that truncates high‐angle to core‐

axis/bedding structures and is associated with intense decarbonatization, local orpiment and pyrite

formation (Fig. 16). In rare instances, the preserved array of fault and fractures in these bedding

plane shears zones is consistent with riedel shear geometry. These structures are interpreted to be

associated with gold deposition and represent reactivation of zones of weakness parallel to bedding

planes.

SUMMARY

Scanning electron microscopy mineral mapping completed on 6 polished thin sections of Au

mineralized samples demonstrates the presence of several ore fluid processes that are analogous to Carlin‐

style mineralization including decalcification, decarbonatization, argillization and associated silicification of

calcareous siltstone. Arsenian fuzzy pyrite and disseminated arsenian pyrite in zones of decarbonatization

are likely a host of Au in siltstone‐hosted mineralization. Collectively, the data presented support the


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interpretation of Au mineralization at the Erika property to be a Carlin‐style target. Future work should focus

on delineating the location and orientation of controlling mineralizing structures in order to more effectively

assess the scope of Au bearing zones identified to date.

References

Cline, J.S., Hofstra, A.H., Muntean, J.L., Tosdal, R.M and Hickey, K.A. 2005. Carlin‐type gold deposits in

Nevada: Critical geological characteristics and viable models. Economic Geology, Vol. 100, 451 ‐ 484.

Fonseca, A., 2007. Technical report on exploration results for the Erika high sulphidation gold property,

Guerrero State, Mexico, 45p.

Leach, T.M., and Corlett, G., 1996, Interim field report on the Erika Prospect, Guerrero State,

Mexico, Internal report for Almaden Resources, 8 p.


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Documents

SEM and Gold deportment study - Geology/GIS …geomantiacogs.com/wp-content/uploads/2015/04/ER_SEM...Sediment‐hosted gold mineralization was recently discovered on Erika property,