Key Information:
- Updated Mineral Resource estimate for Plomosas mine totals 941,000 tonnes @ 13.0% Zn and 3.4% Pb for 154,000 tonnes of contained metal in Indicated and Inferred categories.
- 40% of 2020 plant feed was mined from outside of the existing model.
Consolidated Zinc Limited (ASX:CZL; “Consolidated Zinc” or “the company”) is pleased to announce its updated Mineral Resource estimate for its Plomosas zinc-lead-silver project in northern Mexico.
The resource estimate, independently completed by Ashmore Advisory Pty Ltd (“ASH”) in compliance with the JORC (2012) reporting guidelines, contains 941,000 tonnes @ 13.0% Zn and 3.4% Pb for 154,000 tonnes of contained metal in Indicated and Inferred categories.
This is a decrease of 2.4% of resource tonnage and 3.7% contained zinc metal over the previous resource estimate announced to the ASX on 29 April 2020. The reduction in Mineral Resource derives from the depletion of the geological models of the Level 7 Semi-oxide (“SOX”) mineralised zones for mining conducted during 2020.
Of significant importance is that some 40% of the 2020 production was mined from stopes outside of the existing Mineral Resource however, current data is not sufficient for inclusion in the updated Mineral Resource.
Table 1 details the Mineral Resources by area and category, the locations of which are illustrated in Figure 2.
Mineral Resource Details and Parameters
Results of the independent Mineral Resource estimate by ASH for the Project are tabulated in the Statement of Mineral Resources in Table 1. The Statement of Mineral Resources is reported in accordance with the requirements of the 2012 JORC Code and is therefore suitable for public reporting.
The Mineral Resource is reported above a cut-off grade of 3% Zn which was based on the mining cut-off grade for the operation.
Note: The Mineral Resource has been compiled under the supervision of Mr. Shaun Searle who is a full-time employee of ASH and a Member of the AIG. Mr. Searle has sufficient experience that is relevant to the style of mineralisation and type of deposit under consideration and to the activity that he has undertaken to qualify as a Competent Person as defined in the JORC Code.
All Mineral Resources figures reported in the table above represent estimates in March 2021. Mineral Resource estimates are not precise calculations, being dependent on the interpretation of limited information on the location, shape and continuity of the occurrence and on the available sampling results. The totals contained in the above table have been rounded to reflect the relative uncertainty of the estimate. Rounding may cause some computational discrepancies.
The Mineral Resource has been estimated in accordance with the 2012 Edition of the ‘Australasian Code for Reporting of Exploration Results, Mineral Resources and Ore Reserves’ prepared by the Joint Ore Reserves Committee of The Australasian Institute of Mining and Metallurgy, Australian Geoscientists and Minerals Council of Australia (The JORC Code 2012).
A detailed discussion of the methodology and parameters used in estimating the Mineral Resources is provided in sections below along with an analysis of drilling, sampling and laboratory procedures and QA/QC protocols.
In summary:
- Ordinary Kriging (OK) was used to estimate average block grades using SURPAC software and parameters derived from modelled variograms. Parent block sizes were 10m x 5m x 2.5m;
- Linear grade estimation was deemed suitable due to the geological control on mineralisation. Maximum extrapolation of wireframes from drilling was 20m along strike and 30m down-dip;
- The Mineral Resource estimate has been constrained by the wireframed mineralised envelope, is undiluted by external waste and reported above a Zn cut-off grade of 3%;
- The Mineral Resource was classified as Indicated and Inferred Mineral Resource based on data quality, sample spacing, and lode continuity. The Indicated Mineral Resource was defined within areas of close spaced diamond drilling of less than 20m by 20m, and where the continuity and predictability of the mineralised units was assisted with development drives, along with mapping and channel sampling to assist with structural interpretation. The Inferred Mineral Resource was assigned to areas where drill hole spacing was greater than 20m by 20m and less than 40m by 40m; where small, isolated pods of mineralisation occur outside the main mineralised zones, and to geologically complex zones.
Geology and Geological Interpretation
Level 7
Mineralisation in the Level 7 SOX is structurally controlled with a plunge component of approximately 20o– 30o to the southeast along a shallow dipping plane defined by the Mina Vieja Manto unit. Economic mineralisation in this system is coincident with flexures that host the thicker, high grade mineralisation.
The Level 7 Resource represents sulphide mineralisation that has been affected by late-stage oxidation by oxygenated water flowing through localised faulting. This manto-style sulphide mineralisation is present as ‘kernels’ within rinds of oxidised sulphides which can require a different metallurgical process to that of pure fresh sulphides as found in the Tres Amigos Resource.
Structural mapping at the Level 7 SOX has confirmed that these northeast faults have moved and jostled ore blocks up and down along the strike direction, making extraction of ore a challenging exercise. The relative movement of these blocks is no more than three to four metres in the vertical direction, as illustrated in Figure 4.
Additional Work Program
During 2020 Plomosas mine was visited by a senior structural geologist who worked with the local exploration team on gold exploration and base metal targeting. At the north end of the Level 7 SOX mineralisation a major post deposition sub-vertical fault-oriented WNW-ESE with an offset of 130m to 150m horizontally. This theory will be tested in 2021 and if true the Level 7 SOX mineralisation may continue along strike with the minor faults jolting the in the NE-SW direction.
Any future drilling will focus on converting additional resources from Inferred to Indicated, and infill drilling at the Tres Amigos Resource Level 10 high grade zone and in the SOX below 900mRL that is 25m above Level 9 at 875mRL. The SOX may continue to Level 10 so once the mine is dewatered below Level 10 the SOX will be tested for continuity down dip.
That 40% or 14,056 tonnes of high-grade mineralisation was mined outside of the Mineral Resource estimate indicates that more drilling is required to delineate zones of mineralisation observed in close proximity to underground development. There are opportunities for tonnage increases with additional drilling. During 2021 and 2022 our geological team will address this potentially exciting prospect.
Detailed Discussion of Resource Estimation Methodology and Parameters
Sampling and Sub-Sampling Techniques
Sampling of cut channels was conducted by locating a one metre sampling line, using spray paint across mineralisation and ensuring that the line began in hanging wall host, spanned mineralisation and terminated in footwall host. Where mineralisation was thicker than one metre, the line was adjusted accordingly. This was done to minimise the bias of the sample value. Channel sampling was then completed, using the line as a guide, without sampling the line itself. As much representative sample was taken from the length of the line to produce a two to four-kilogram sample. For this level of exploration, the sample size and method of sampling was deemed adequate to represent in-situ material.
Sampling techniques employed at the Plomosas underground drilling program include saw cut NQ drill core samples. Diamond NQ3 core was sampled on geological intervals/contacts, with the minimum sample size of 0.5m and max 1.2m. Core was cut in half, with one half to be sent for analysis at an accredited laboratory, while the remaining half was stored in appropriately marked core boxes and stowed in a secure core shed. Duplicates were quarter core, sampled from the half sent for analysis.
Drilling Techniques
NQ triple tube core (NQ3) is currently being used to drill out the geological sequences and identify zones of mineralisation that may or may not be used in any Mineral Resource estimations, mining studies or metallurgical testwork.
Sample Analysis Method
All drill samples were submitted to ALS Laboratories in Chihuahua City for sample preparation with sample pulps sent to ALS in Toronto, Canada for multi-element analysis using a 30g charge with a multi-acid digest and ICP-MS or AAS finish (ME-ICP61). Over the limit results were routinely re-assayed by ore grade analysis OG62. Over the limit results for the ore grade were re-assayed by titration methods Cu-VOL61, Pb-VOL50 or Zn-VOL50.
Analyses include 51 elements and include Ag, Au, Cu, Pb, Zn as the main elements of economic interest. The methods and procedures are appropriate for the type of mineralisation and the techniques are considered to be total.
Estimation Parameters
Using parameters derived from modelled variograms, Ordinary Kriging (OK) was used to estimate average block grades in three passes using SURPAC software. Linear grade estimation was deemed suitable for the Plomosas Mineral Resource due to the geological control on mineralisation. Maximum extrapolation of wireframes from drilling was 20m along strike and 30m down-dip. This was equal to the drill hole spacing in these regions of the Project. Maximum extrapolation was generally half drill hole spacing.
The parent block dimensions used were 10m NS by 5m EW by 2.5m vertical with sub-cells of 0.625m by 0.625m by 0.625m. The model was rotated to align with the strike of the mineralisation on a bearing of 330°. The parent block size dimension was selected on the results obtained from Kriging Neighbourhood Analysis that suggested this was the optimal block size for the dataset.
The deposit mineralisation was constrained by wireframe solids constructed using a nominal 2% combined Zn and Pb cut-off grade with a minimum down-hole length of 1m. The wireframes were applied as hard boundaries in the estimate.
Statistical analysis was carried out on data from 53 domains. After review of the project statistics, it was determined that high grade cuts for Ag within two domains were necessary. The cut applied was 300g/t Ag resulting in two composites being cut.
An orientated ‘ellipsoid’ search was used to select data and adjusted to account for the variations in lode orientations, however all other parameters were taken from the variography derived from Domain 1. Up to three passes were used for each domain. The first pass had a range of 30m, with a minimum of 6 samples. For the second pass, the range was extended to 50m, with a minimum of 4 samples. For the final pass, the range was extended to 100m, with a minimum of 2 samples. A maximum of 16 samples was used for all three passes.
It is assumed that the bulk density will have some variation within the mineralised material types due to the host rock lithology and sulphide minerals present. Therefore, a regression equation for Zn and density was used to calculate density in the block model.
Validation of the model included detailed comparison of composite grades and block grades by strike panel and elevation. Validation plots showed good correlation between the composite grades and the block model grades.
Mineral Resource Classification Criteria
The Mineral Resource estimate is reported here in compliance with the 2012 Edition of the ‘Australasian Code for Reporting of Exploration Results, Mineral Resources and Ore Reserves’ by the Joint Ore Reserves Committee (JORC). The Mineral Resource was classified as Indicated and Inferred Mineral Resource based on data quality, sample spacing, and lode continuity. The Indicated Mineral Resource was defined within areas of close spaced diamond drilling of less than 20m by 20m, and where the continuity and predictability of the mineralised units was assisted with development drives, along with mapping and channel sampling to assist with structural interpretation. The Inferred Mineral Resource was assigned to areas where drill hole spacing was greater than 20m by 20m and less than 40m by 40m; where small, isolated pods of mineralisation occur outside the main mineralised zones, and to geologically complex zones
Cut-off Grade, Mining and Metallurgy Methods and Parameters Considered to Date
The Statement of Mineral Resources has been constrained by the mineralisation solids and reported above a Zn cut-off grade of 3%. The cut-off grade was estimated based on current mining cut-off grades for the operation.
This announcement was authorised for issue to the ASX by the Directors of the Company. For further information please contact:
Brad Marwood
Managing Director
08 9322 3406
ABOUT CONSOLIDATED ZINC
Consolidated Zinc Limited (ASX: CZL) owns 100% of the historic Plomosas Mine, located 120km from Chihuahua City, Chihuahua State, Mexico. Chihuahua State has a strong mining sector with other large base and precious metal projects in operation within the state. Historical mining at Plomosas between 1945 and 1974 extracted over 2 million tonnes of ore grading 22% Zn+Pb and over 80g/t Ag. Only small-scale mining continued to the present day and the mineralised zones remain open at depth and along strike.
The company has commenced mining at Plomosas and is committed to exploit the potential of the high-grade Zinc, Lead and Silver Mineral Resource through the identification, exploration and exploitation of new zones of mineralisation within and adjacent to the known mineralisation with a view to identify new mineral resources that are exploitable.
Competent Persons’ Statement
The information in this report that relates to exploration results, data collection and geological interpretation is based on information compiled by Duncan Greenaway (Hons), Mr Greenaway is a Member of the Australasian Institute of Mining and Metallurgy (AusIMM). Mr. Greenaway has sufficient experience that is relevant to the style of mineralisation and type of deposit under consideration and to the activity that is being undertaken to qualify as Competent Person as defined in the 2012 edition of the ‘Australasian Code for Reporting of Exploration Results, Minerals Resources and Ore Reserves’ (JORC Code). Mr. Greenaway consents to the inclusion in the report of the matters based on his information in the form and context in which it appears.
The information in this report that relates to Mineral Resources is based on information compiled by Mr Shaun Searle who is a Member of the Australasian Institute of. Mr Searle is a full-time employee of Ashmore Advisory Pty Ltd. Mr Searle has sufficient experience which is relevant to the style of mineralisation and type of deposit under consideration and to the activity which he has undertaken to qualify as a Competent Person as defined in the 2012 Edition of the ‘Australasian Code for the Reporting of Exploration Results, Mineral Resources and Ore Reserves’. Mr Searle consents to the inclusion in this report of the matters based on his information in the form and context in which it appears.
Original Article: https://www.consolidatedzinc.com.au/wp-content/uploads/2021/03/20210318-Mineral-Resource-Update-FINAL-ASX-LODGEMENT.pdf
