REG - Great Southrn.Copper - Cerro Negro Drilling Confirms Outstanding Grades

Great Southern CopperAnnouncement

12/06/2025 07:10

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RNS Number : 5588M  Great Southern Copper PLC  12 June 2025

 

THIS ANNOUNCEMENT CONTAINS INSIDE INFORMATION AS STIPULATED UNDER THE UK
VERSION OF THE MARKET ABUSE REGULATION NO 596/2014 WHICH IS PART OF ENGLISH
LAW BY VIRTUE OF THE EUROPEAN (WITHDRAWAL) ACT 2018, AS AMENDED.  ON
PUBLICATION OF THIS ANNOUNCEMENT VIA A REGULATORY INFORMATION SERVICE, THIS
INFORMATION IS CONSIDERED TO BE IN THE PUBLIC DOMAIN.

 

12 June 2025

 

Great Southern Copper plc

("GSC" or the "Company")

 

First Assay Results from Phase II Drilling at Cerro Negro Confirm Outstanding
Cu-Ag Grades

Drillhole CNG25-DD013 Intersected up to 4% Cu and 578 g/t Ag

 

Exploration holes confirm significant extension of high-grade Cu-Ag system
south of Mostaza

 

 

Great Southern Copper plc (LSE: GSCU), the company focused on
copper-gold-silver exploration in Chile, is extremely pleased to report
high-grade assay results from Phase II diamond drilling at the Mostaza Mine,
Cerro Negro.

 

Highlights:

·    Assay results received for holes CNG25-DD010 - DD014 with significant
intervals including;

Ø DD013: 5m @ 3.04% Cu and 322.4 g/t Ag from 37m, within a broader zone of

§ 13.9m @ 1.74% Cu and 153.4 g/t Ag from 26.1m

Ø DD012: 3m @ 3.43% Cu and 164.7 g/t Ag from 24m, within a broader zone of

§ 20m @  32.1g/t Ag from 7m (copper and silver leached in surface oxide
zone)

Ø DD010: 19m @ 30.5g/t Ag from 6m, including

§ 8.8m @ 58g/t Ag from 10.2m (copper and silver leached in surface oxide
zone)

·    CNG25-DD012 confirms mineralisation up to 500m south of the Mostaza
mine

·   Exploration holes DD010, DD012 and DD014 intersected broad zones of
anomalous silver in silicified leached rock near surface stongly indicative of
the potential for high-grade sulphide Cu-Ag mineralisation  at depth

·    Phase III drilling is planned to target beneath the broad leached
mineralisation zones

·  Pole-dipole induced polarisation (PDIP), gradient, and audio frequency
magneto-telluric (AMT) geophysical surveys are underway in advance of Phase
III drilling

·    Further assays pending on holes CNG25 DD015 - DD025

·    GSC holds option to own 100% of the Cerro Negro project including the
Mostaza mine

·    Prospect located at low elevation with excellent access to
infrastructure and mining services

 

 

Sam Garrett, Chief Executive Officer of Great Southern Copper, said:

"The exciting results at Mostaza continue with drilling below the historical
Mostaza mine intersecting further outstanding high-grade Cu-Ag mineralisation
that remains open along strike and at depth.

 

"In addition, our exploration drilling, designed to test for mineralisation
beyond the historical pit, also intersected significant mineralisation over
500 metres south of the mine. Holes DD010, 012 and 014 have intersected broad
zones of anomalous silver hosted in highly leached rocks near surface, which
we believe represent the possible oxidised tops of sulphide-rich, high-grade
Cu-Ag mineralised lens material at depth.

 

"Our very exciting drill results, together with the recently started
geophysical surveys, preliminary petrography, and metallurgical test work, are
setting the stage for an exciting Phase III drill programme.

 

"We look forward to sharing more exciting results as they become available."

 

 

Results of diamond drillholes CNG25 DD010 - DD014

 

Phase II diamond drilling was designed to test continuity of the high-grade
mineralisation intercepted in Phase I drilling at the Mostaza mine and to test
new areas along strike to the north and south (see Figures 1, 2, 3).

 

Drillhole CNG25-013 was drilled along strike to the south of and roughly
parallel to Phase I drillhole CNG25-DD001 that intersected 20m @ 3.31 % Cu and
269.9 g/t Ag from 27m, including 7m @ 5.72 % Cu and 489.6 g/t Ag from 31m(1)
(see Figure 3).

 

Hole DD013 intercepted abundant disseminated and crackle-hosted
chalcocite-dominant mineralisation in strongly altered and locally brecciated
"lens" rock (see Figure 4). Assay results returned 13.9m @ 1.74% Cu and 153.4
g/t Ag from 26.1m, including 5m @ 3.04% Cu and 322.4 g/t Ag from 37m, and a
highest grade of 1m @ 4% Cu and 578 g/t Ag from 30m. Table 1 summarises the
Phase I and II significant intercepts to date.

 

These results are continuing to add to GSC's understanding of the architecture
of the mineralised system at Mostaza, with updated modelling and
interpretation suggesting that the high-grade mineralisation intersected in
holes DD001, DD003, DD005 and DD013 (see Figures 2 - 3) is not part of the
subvertical Lens 2 that outcrops in the mine - which was the focus of
historical mining and resource estimation and GSC's original drill targeting.
Instead, the information provided by new drilling  suggests that GSC may have
discovered the top of a previously unrecognised tabular body (or "manto")
dipping at some 50° degrees to the west. Importantly the manto is untested,
close to surface, and open at depth and along strike.

 

Drillhole CNG25-DD011 was drilled to the north of the Mostaza open pit to test
for a possible strike extension of Lens 2. Although the hole cut numerous
intervals of alteration (Figure 4) with anomalous values of Cu and Ag, no
high-grade mineralisation was cut, suggesting Lens 2 may have "pinched out"
along strike or it could have been offset by a fault.

 

Exploration drillholes CNG25-DD010, 012 and 014 tested strike extensions of
the Mostaza style mineralisation up to 500 metres south of the mine, where
large outcrops of silicified structurally controlled mineralisation are mapped
as Lens 4 (Figure 1 and 2). Historical artisanal mining of this southern lens
is evident, however, no historical details of the workings, nor tonnages or
grades are available. All drillholes intersected zones of strongly oxidised,
structurally-controlled silicification over varying widths. Significant assays
are summarised in Table 1.

 

Hole DD012 is the southernmost hole drilled to date. It intersected
approximately 22.5 metres of strongly oxidised "lens" and "proto-lens" from
surface with consistently anomalous but low-grade Cu and Ag thought to have
been depleted by intense near-surface leaching. The leached interval
transitions abruptly to hypogene sulphide mineralisation with 3m @ 3.43 % Cu
and 164.7 g/t Ag which may reflect pre-leaching grades in the oxide zone (see
Figure 5).

 

Hole 010 intersected similar intensely oxidised and leached rock (see Figure
4) strongly depleted in Cu but consistently anomalous in Ag (19.0m @ 30.5 g/t
Ag from 6.0m) suggesting potential for higher grades of copper and silver at
depth. The hole also intersected shallow underground mine workings from 10.2 -
14.2m down-hole. This is highly encouraging for a deeper exploration hole into
the interpreted sulphide zone below.

 

Phase III drilling

 

The next planned phase of drilling will test this promising lens 3 - 5 area
for high-grade mineralisation at depth below the leached oxide zone and
historical workings as well as testing other exploration targets further to
the south where rock chip samples by GSC have reported highly anomalous copper
and silver in outcrop(2).

 

Figure 1: Cerro Negro Project, Mostaza Mine. Plan view showing the open pit
and extensions of mineralisation at depth and to the south. Drillholes in this
release are labelled.

 

 

Figure 2: Cerro Negro Project, Mostaza Mine. Long section looking east showing
the projection of mineralised bodies at depth. Note the recently interpreted
"Manto" beneath the open pit. Arrows indicate that mineralisation remains
open. Holes in this release are labelled.

 

Figure 3: Cerro Negro Project, Mostaza Mine. Long section orthogonal to Manto
1 showing the location of reported Phase I and Phase II drill holes. The blue
box shows the intercepts in this release.

 

Figure 4. Cerro Negro Project, Mostaza Mine. Photograph of core from hole
CNG25 DD013 on the left and CNG25 DD010, 011 and 012 on the right, with grades
of Cu % and Ag g/t.

 

Figure 5: Hole CNG25 DD012, core illustrating the sharp transition from
oxidised leached core (with anomalous silver) to primary, sulphide-rich lens
material with high-grade copper-silver mineralisation at 24m depth down-hole.

 Hole_ID           From    (m)     To         (m)          Interval (m)  Cu         (%)          Ag        (g/t)         Sb    (ppm)

 CNG25 DD001       27              47                      20            3.31                    269.9                   934
              inc  31              38                      7             5.72                    489.6                   1085
              inc  35              38                      3             6.62                    562.7                   407

 CNG25 DD002       38.9            43.1                    4.2           1.73                    126.5                   824

 CNG25 DD003       36.6            55.2                    18.6          1.85                    146.6                   798
              inc  39              52                      13            2.48                    198.1                   1049
              inc  48              51                      3             3.31                    254.7                   1608
              inc  50              51                      1             4.64                    406                     2150

 CNG25 DD004       no significant intercepts

 CNG25 DD005       35              56                      21            2.9                     246.7                   978
              inc  37              52                      15            3.79                    328.4                   1252
              inc  40              52                      12            4.24                    369.5                   1279
              inc  45              52                      7             5.08                    449.6                   1309
              inc  45              47                      2             6.05                    547.5                   645

 CNG25 DD006       132.54          132.91                  0.46          0.08                    24.9                    5.48

 CNG25 DD007       87              120                     33            1.96                    60.6
              inc  88              91.85                   3.85          5.21                    318
              and  115             120                     5             5.59                    99.2
              inc  116.4           118.9                   2.5           9.67                    175.4

 CNG25 DD008       0               31                      31                                    7.1
              inc  0               1.2                     1.2           0.512                   31.3                    28
              and  8               22                      14                                    9.6

 CNG25 DD009       Oxide zone - no significant intercept

 CNG25 DD010       6               25                      19                                    30.52
              inc  10.2            19                      8.8                                   58.02                   62.9
              and  18              23                      5             0.31                    23.7

 CNG25 DD011       Oxide zone - no significant intercept

 CNG25 DD012       7               24                      17                                    8.7                     Oxide
              inc  16              24                      8                                     13.1                    Oxide
                   24              27                      3             3.43                    164.7                   39.6

 CNG25 DD13        26.1            40                      13.9          1.74                    153.4                   44.2
              inc  26.1            34                      7.9           2.35                    227.6
              inc  29              32                      3             3.54                    405.3

 CNG25 DD014       Oxide zone - infill sampling results pending

 

Table 1: Summary of significant intercepts for Phase I and Phase II drill
holes.

 

About the Mostaza Cu-Ag deposit, Cerro Negro Project

 

High-grade Cu-Ag mineralisation at Cerro Negro is hosted by structurally
controlled elongate lodes of variable width (<4-20m) that strike between
north and north-east. Historical mining at the Mostaza mine exploited steeply
dipping to subvertical lodes such as "Lens 2". In addition to the steeply
dipping "lenses", geological interpretation of recent drill results has
identified a previously unrecognised and untested tabular lode, or "manto",
below the Mostaza pit and dipping about 50 ° to the west.

 

Copper-silver mineralisation in the lenses and manto comprises abundant
disseminations, veinlets, crackle networks and breccia matrix fillings of
hypogene chalcocite with lesser tennantite, digenite, bornite, chalcopyrite,
pyrite and local galena and sphalerite. The chalcocite contains inclusions of
stromeyerite, an Ag-Cu sulphide.

 

Host rocks to mineralisation comprise multiple generations of intensely
altered breccia, tuffisite and felsic intrusive. In the mine, the mineralised
lodes are bound to the east and west by faults that are typically invaded by
narrow (1-2m) andesite to rhyolite dykes. Outside of the bounding dykes and
faults, the enclosing wall rocks consist of an east-dipping bedded sequence of
fresh volcanic lava flows and brecciated dacite that might be part of a large
dome-diatreme complex outcropping to the east.

 

In addition to the mineralisation seen in the Mostaza mine, several Cu-Ag rich
bodies have been mapped at surface.  Historically these were interpreted as
discrete "lenses", but collectively they have the potential to form an
anastomosing network of mineralised bodies continuous over a strike length of
up to 2km or more.

 

Core preparation, sampling and assaying

 

The Cerro Negro diamond drill core is collected from site by GSC staff and
transported to the Company's nearby sampling facilities where it is then
processed for geological, geotechnical, petrophysical and geochemical data.
Sampling intervals are selected principally on geologic boundaries and may
vary in length up to 2m. The core is cut into two halves using an electric
diamond brick saw with half-core samples each allocated a unique identifier
code and bagged-tagged separately. Samples for each complete hole are
transported by GSC personnel to ALS laboratories in Santiago, Chile for sample
preparation (drying, weighing, crushing and grinding). A final 200g aliquot of
each sample is forwarded by ALS to their laboratories in Lima, Peru where it
is assayed for Au (by 30g fire assay with ICP-AES finish method) plus a suite
of 48 base metals and trace elements including Cu and Mo (by four acid digest
ICP-MS method).

 

Sampling and assaying QAQC protocols employed by the company for this drilling
project include routine insertion of standard reference materials including
standards and blanks. Results for each SRM is assessed to monitor the accuracy
and precision of the assay data from ALS for the core samples.

 

Cautionary note:

The Company cautions that all references to "resources", "mineral resources",
or "mineral resource estimates" in this RNS are historical and were prepared
and reported prior to the implementation of the JORC code and therefore are
non-JORC compliant. The Company advises that the resource categories used in
the historical estimates, for example "measured, indicated, demonstrated and
inferred", may not have the same meaning or degree of confidence as current
JORC categories. Historical records indicate that the quoted non-JORC
resources were calculated using the polygonal method based on underground
sampling, 1024m of drilling in 25 holes, and geological cross-sections and
level plans. GSC is presenting this information for historical context only
and is not treating it as a current mineral resource estimate.

References to mineralised grade intervals in drill holes are considered
apparent thicknesses as there is not sufficient geological information to
calculate true thickness of mineralised intercepts at this time.

 

References:

1.            RNS 5182Y (26 February 2025): Cerro Negro assays
return 20m of 3.3% Cu & 270g/t Ag

2.            RNS 5192G (29 April 2025): Exploration results extend
Cerro Negro

 

Enquiries:

 

 Great Southern Copper plc
 Sam Garrett, Chief Executive Officer  +44 (0) 20 7138 3204

 SI Capital Limited
 Nick Emerson                          +44 (0) 1483 413500

 BlytheRay
 Tim Blythe / Megan Ray                +44 (0) 20 7138 3204

 

Notes for Editors:

 

About Great Southern Copper

 

Great Southern Copper PLC is a UK-listed mineral exploration company focused
on the discovery of copper-gold deposits in Chile. The Company has the option
to acquire rights to 100% of two projects in the under-explored coastal belt
of Chile that are prospective for large scale copper-gold deposits. Chile is a
globally significant mining jurisdiction being the world's largest producer
and exporter of copper.

 

The two, early-stage Cu-Au projects comprise Especularita and San Lorenzo
Projects, both located in the coastal metallogenic belt of Chile which hosts
significant copper mines and deposits, including Teck's Carmen de Andacollo
copper mine, and boasts excellent access to infrastructure such as roads,
power and ports. Significant historical small-scale and artisanal workings for
both copper and gold are readily evident in both exploration project areas.
The coastal belt offers deposit type optionality for copper including porphyry
and IOCG style deposits as well as newly recognised intrusive-related copper
and gold deposits.

 

Great Southern Copper is strategically positioned to support the global market
for copper - a critical battery metal in the clean energy transition around
the world. The Company is actively engaged in exploration and evaluation work
programmes targeting both large tonnage, low to medium grade Cu-Au as well as
high-grade Cu-Ag-Au deposits.

 

Further information on the Company is available on the Company's
website: https://gscplc.com (https://gscplc.com/)

 

Competent Person Statement

 

The information in this announcement that relates to exploration results is
based on and fairly represents information reviewed or compiled by Mr Sam
Garrett, a Competent Person who is a Member of the Australian Institute of
Geoscientists and a Fellow of the Society of Economic Geologists. Mr Garrett
is the CEO and a shareholder of Great Southern Copper PLC. Mr Garrett has
sufficient experience that is relevant to the styles of mineralisation and
types of deposit under consideration and to the activity being undertaken to
qualify as a Competent Person as defined in the 2012 Edition of the
"Australasian Code for Reporting of Exploration Results, Mineral Resources and
Ore Reserves". Mr Garrett has provided his prior written consent to the
inclusion in this announcement of the matters based on information in the form
and context in which it appears.

 

This announcement includes information that relates to Exploration Results
prepared and first disclosed under the JORC Code (2012) and extracted from the
Company's previous LSE announcements as noted, and the Company's Prospectus
dated 20 December 2021. Copies of these announcements are available from the
LSE Announcements page of the Company's website: www.gscplc.com.

 

The Company confirms that it is not aware of any new information or data that
materially affects the information included within the Prospectus dated 20
December 2021.

 

Forward Looking and Cautionary Statements

 

Some statements in this announcement regarding estimates or future events are
forward-looking statements. They include indications of, and guidance on,
future earnings, cash flow, costs and financial performance. Forward-looking
statements include, but are not limited to, statements preceded by words such
as "planned", "expected", "projected", "estimated", "may", "scheduled",
"intends", "anticipates", "believes", "potential", "predict", "foresee",
"proposed", "aim", "target", "opportunity", "could", "nominal", "conceptual"
and similar expressions. Forward-looking statements, opinions and estimates
included in this report are based on assumptions and contingencies which are
subject to change without notice, as are statements about market and industry
trends, which are based on interpretations of current market conditions.
Forward-looking statements are provided as a general guide only and should not
be relied on as a guarantee of future performance. Forward-looking statements
may be affected by a range of variables that could cause actual results to
differ from estimated or anticipated results and may cause the Company's
actual performance and financial results in future periods to materially
differ from any projections of future performance or results expressed or
implied by such forward-looking statements. So, there can be no assurance that
actual outcomes will not materially differ from these forward-looking
statements.

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