Kidd Creek Mine: OMET Deep Technology Demonstration

Executive summary

Introduction

As part of the Ontario Minerals Exploration Technologies Program (OMET), Quantec performed a demonstration survey of a new deep exploration geophysical technology (Titan) for Falconbridge Limited at their Kidd Creek Mine Site near Timmins, Ontario. The survey was carried out in December of 2001 and was funded by OMET, Falconbridge and Quantec.

The Titan system is a multi-channel, distributed acquisition survey, recording broad band Magnetotelluric data (AMT/MT), D.C. Resistivity data and Induced Polarization data. The Titan system provides high multiplicity data sets utilising 24bit Sigma Delta Time series Full waveform data, consists of 3 main elements: 1) its acquisition system, 2) its digital signal processing, and 3) its 2D-3D interpretation capability.

Survey Objectives

The primary objectives of this demonstration survey are:

1. 1. To demonstrate and evaluate the Titan system’s capability of mapping geology and detecting anomalous mineralization (massive or disseminated) in areas of thick overburden and Palaeozoic cover within Ontario’s complex environment.
2. To demonstrate Titan system capabilities within a noise-contaminated mine-site environment.
3. To determine within the survey area if the new geophysical results support any additional drilling

Procedures

To maximise the effectiveness of the survey results, a scientific process was followed (3D Quest). This process included the construction of a common earth model within the survey site utilising historical information from the site to provide geological subsurface information. Petrophysical data was collected in order to assign quantitative information to geological formations. The application of this quantitative information within the earth model provided geo-referenced constraints for inverting the Titan MT and DC/IP data. The resulting subsurface resistivity and IP images therefore respect the geological information and areas where differences between the geologic model and the geo-referenced inversion exist, represent distinct areas for follow-up.

Gocad Common Earth Model

• The Gocad geologic model was constructed by interpolating geologic contacts across 6 successive level plans spaced 200-400m apart, from surface to 1.8km depths.
• The geologic information provided by Kidd Creek for the Gocad model includes geologic elements extending 1km east, and 500m further north and south of the existing survey coverage. However, except for overburden thickness information, the known geology does not extend further west than approx. 78+00E, which is 600m east of the westernmost tip of our survey lines ­ and so, beyond this point, a mafic volcanic geology has been assumed for this region of the Gocad model

Petrophysical Analysis

• The available physical property data, required to populate the Gocad model was drawn from several sources, both in-situ (borehole logging data) and indirect (archival laboratory studies and 2D inversions).

2D Sensitivity Analysis

• The Gocad model of the Kidd Creek deposit was used to test the depth of investigation capability of the Titan DCIP and MT surveys, as well as their detection limits using 2D inversion.
• The model allows the simulation of Titan data over a world-class ore body represented from surface to depths of 2km.
• The sensitivity analysis proved that Titan MT would be capable of detecting Kidd Ck. orebody down to 2 km. The DC resistivity should detect and image Kidd Ck. to depths of 500 to 750m. The IP would potentially detect and image the orebody to depths significantly less than 500 metres due to weaker contrasts.

Survey

The survey consisted of 5 lines, each 4800 m long, separated by 200m and with 100m-station interval and located just north of the Kidd open pit. These lines are oriented approximately E – W. The lines run both orthogonal and oblique to the predominant geological strike.

Analysis and interpretation:

1. The data were interpreted quantitatively using computerized inversion codes. The inversions were done in two distinct ways; unconstrained using a mathematical half-space as a starting model and constrained using a geological model as the starting point for the inversion.
2. After obtaining the referenced inversions, the interpretation results are re-introduced into the Gocad model, to precisely target unexplained geophysical responses, using Ratio-M and Delta-M analyses. This allows easy comparison against the geology.
3. Finally, using a combination of cross-sectional and level plans, the unexplained Ratio-M and Delta-M geophysical responses are rated, on the combined basis of anomaly-strength, size, host geology and degree of correlation between MT, DC and IP technologies.

Results

Initial, unconstrained 2D inversions demonstrate excellent correlation between the known geology, buried beneath up to 70m of clay overburden, and curvi-linear zones of resistivity low and chargeability high, which characterize the targeted rhyolitic horizons. However, the constrained inversions have proven the most effective targeting tools for shallow and deep exploration at the Kidd property.

Constrained geo-referenced inversions of the Titan 24 data have significantly improved the results of the survey, providing better detail along, and across the lithologic units and particularly down dip. This has enabled interpretation to depths in excess of 1.5 km. This process has identified a number of significant anomalies, which have been prioritised into three groups. Priority was determined by size, host rock lithology, strength and degrees of correlation. These are all concentrated along the key Rhyolitic horizons.

The results of this survey are summarized:

• The system delineated responses on each line that are unexplained in the geological model. Several of these anomalies are consistent with the response of massive sulphide or graphite mineralization.
• Specific to the Kidd property the system responded as follows;
  • AMT/MT has proven to be the most reliable indicator of conductivity thickness variations both along strike and down dip of the Rhyolitic units. Benefiting from superior depth-penetration (>1.5 km+) and advanced interpretation algorithms, the MT inversion results, in particular, have identified deep anomalies of interest within the north Rhyolite horizon. These anomalies appear to be the most compelling signatures identified in the Titan 24 surveys at Kidd Creek. There are five high-priority deep anomalies (>750m) associated with 2 to 3 distinct targets along strike identified within the survey volume. All are situated along the north Rhyolite. This includes a deep anomaly centred on line 11400N at 1.5km depth.
  • Other deep conductive anomalies have been identified along other Rhyolitic units such as the Chance horizon, however they are comparatively weaker and do not have the same depth extent and hence have been assigned a lower priority.
  • A larger number of high priority signatures have been identified within the near surface (<250m). These anomalies tend to be small (<100x100m) but they represent high chargeability, DC and MT low resistivity.
  • In the mid depth range (250-750m) there are five additional high priority anomalies. These have been identified using primarily the DC and MT resistivity.
  • The IP parameter, as predicted by the 2D forward modelling sensitivity analysis, seems to provide reliable information on targets to approximately 350m depths. Similarly, there is good correlation between the DC resistivity and the MT resistivity to depths of 500-750m. Below these depths Titan MT is the only effective exploration tool.

Conclusions

1. This survey successfully demonstrates the capability of the Titan system to map geology and anomalous mineralization below thick overburden. Anomalies and targets have been identified to depths in excess of 1.5 km.
2. The Titan system was capable of this depth of exploration in the noise environment of the Kidd Mine site.
3. The interpreted results require evaluation against the known drill and downhole EM database. Any un-drilled high priority targets should be evaluated for future drilling.

At present, the exploration objectives have all been favorably answered, using the Titan-24 distributed acquisition technology and integrated geologic and geophysical interpretation. The Titan system is a viable exploration tool in the mine site environment and in areas of deep conductive cover.

This scientific approach to deep earth imaging provides a significant advanced means by which to focus drill programs, and is a cost-effective approach both to identifying drill targets, focusing drill programs and sterilizing ground. The Titan/Quest approach is a systematic methodology for integrating and reconciling all of the available information. The purpose is a dramatically improved and integrated exploration program.

Recommendations at Kidd

The Titan-24, 3D-Quest, approach has three valuable applications for property evaluation in the Kidd Creek Mine district: A) Sterilizing ground - drilling budgets not wasted, B) Guiding drill target designation - improving success rates, and C) Accountable and scientific Re-analysis of geophysical results during and post-drilling to minimize follow-up holes. In addition, the following points should be addressed for this project.

• Many indications of zones of anomalous conductivity and chargeability, within & along the rhyolitic bands, as well as within the country rocks, remain to be explained. Specifically, the Titan 24 anomalies need to be reconciled with/against the diamond drill and borehole EM database.
• The Gocad model should be queried for fully integrated drill targets. (Other elements for the query may include geochemistry, assays, depth, etc.)
• Quantec and Falconbridge should work together to assess and prioritise anomalies that have not yet been drilled.
• Additional physical property data should be collected to more accurately quantify all the units in the Gocad earth model. i.e. such as rhyolite, massive sulphide, graphite and possibly overburden. This will provide improved confidence in the constrained inversions and anomalies defined.

 

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