Geological continuity in the context of resource modeling and estimation usually refers to the lithological (sometimes structural) features that define the ore zone with a defined consistency. This might be defined, for example, by a particular sandstone unit which consistently hosts uranium mineralization over a certain area, a vein (ore shoot) hosting gold mineralization or even a contact area between to rock types (skarn deposit). Value continuity however, is defined as the degree of consistency with which the value of the mineralization itself is consistent within a particular deposit. This value speaks of grade, thickness and could even be extended to geo-metallurgical consistency (the continuity of similar mineralogy). But why do we need to differentiate between these two concepts as opposed to just pure continuity?
The corner stone of every feasibility study or mining project is a robust resource model/ estimation and in turn, the foundation of such an estimation is the quality of the primary data that was used as input for the model. As we have all heard, “rubbish in, rubbish out”. This primary data refers to the logs and analytical samples of drill core (or chips). The quality and perspective (oddly enough) with which core logging is completed can have a significant effect on the resource estimation of a deposit. Naturally the further from accurate the quality is, the increasingly devastating it can be. Something that can have a rather unexpected effect on mine planning and later on project execution, is the aforementioned perspective with which logging is done. I will elaborate in a moment.
Remember, logging and sampling of drill core is at the small end of the “error wedge” ie. a small error at this primary data collection point grows in magnitude further down the value chain of feasibility study. This is due to the incremental accumulation of error through the different activities including human error in logging and data input at any level, analytical error in sampling results, and then inherent error in the final estimation process. Remember, “all models are wrong, but all are helpful”. So as geologists we cannot compromise on primary data quality and the interpretation of the geology at this level. In terms of geological interpretation and especially deposit scale understanding, by the time you are drilling, you should be relatively far down the line though. Drilling is usually a late activity in even fresh greenfields exploration. Strive to be accurate in your logging and allow it to be reviewed. Scrutinize assay results and chew on them. Don’t compromise on quality.
Many geologists are excellent when it comes to this primary technical execution. Few however have a perspective which constantly takes the whole mining value chain into consideration. How will the way your record your data now help the resource modeller, the mine planner or the metallurgist? Yes, you can get lost in the detail, even as a geologist, even in the geology and mineralogy. You can even sometimes be counter-intuitive in the pursuit of quality. This is a valuable skill that every industry geologist should pursue. It is a fine line and takes a little work and self-learning.
As a simple example, I worked on a ultramafic deposit which had been severely metamorphosed and altered resulting in tremolite, chlorite, actinolite, serpentinite, phlogopite schists of widely varying mineral proportions and at constantly varying intervals. This gave rise to over 20 different lithological units all originating from the same protolith dunite. Such accurate but unnecessary data would have kept a resource modeller busy for weeks, a waste of time and money. It must be added that the mineralization was not related to the level of alteration.
Stratigraphic allocation is another geological piece of information which can greatly assist or inhibit mine planning. If we think even further down the value chain to actual mining it often plays a critical role in grade control ore classification. “Stratigraphy” in this context does not only refer to what is found above or below, but more importantly from a mining perspective, how does lithology and mineralization correlate and how effectively can the former be used to guide mining. How practical can we as geologists make it for the loader operator, crew leader or blasting team?
Approach is key and your perspective determines your approach. As you log core approach it as if the deposit will definitely become a operating mine. Have this approach in the way you sample, how you allocate contacts, assign lithology, and mark out the stratigraphy. This kind of approach puts you in a position to add real, long term value to a project, regardless of the current stage it is in. Keep thinking where this thing is going, and in our industry, that is a mine!