I Prospecting and the Exploration Process a review of all available information on the prospect,such as government geo logical mapping and geophysical surveys,the results of previous exploration and the known occurrence of minerals: .preliminary geological interpretations of air photographs and remote sensed TV: ock and soil sampling for geochemistry: ·reg nal and deta led geophysical surveys: drilling aimed at increasing geological knowledge. 1.5.2 Target Drilling This stage is aimed at achieving an intersection of ore potential ore.The testins ally be by r fully targ red diam nd or rotary-percu sion drill holes,b rarely t enchi g.pitti ing a employed. is probably the most critical stage of exploration since,depending on its results,decisions involving high costs and potential costs have to be made If a decision is made that a potential ore body has been located,the costs of explo ration will then dramatically escalate,often at the expense of other prospects.If it is decided to write a prospect off after this stage,there is always the possibility that an ore body has been missed. 1.5.3 Resource Evaluation Drilling This stage provides answers to economic questions relating to the grade,tonnes and mining rgical ch f th body.A good under ineraliza stand. on sh dy have b .4，】卫九其 en achieved stage.Providing the data to answer the economic questions requires detailed patter drilling and sampling.Because this can be such an expensive and time-consuming process,this drilling will often be carried out in two sub-stages with a minor decision point in between:an initial evaluation drilling and a later definition drilling stage. Evaluation and definition drilling provide the detail and confidence levels required to proceed to the final feasibility study. 1.5.4 Feasibility Study This,the final stage in the process,is a desk-top due-diligence study that assesses all fact the Wth very a projects,the costsd
6 1 Prospecting and the Exploration Process • a review of all available information on the prospect, such as government geological mapping and geophysical surveys, the results of previous exploration and the known occurrence of minerals; • preliminary geological interpretations of air photographs and remote sensed imagery; • regional and detailed geological mapping; • detailed rock-chip and soil sampling for geochemistry; • regional and detailed geophysical surveys; • shallow pattern drilling for regolith or bedrock geochemistry; • drilling aimed at increasing geological knowledge. 1.5.2 Target Drilling This stage is aimed at achieving an intersection of ore, or potential ore. The testing will usually be by means of carefully targeted diamond or rotary-percussion drill holes, but more rarely trenching, pitting, sinking a shaft or driving an adit may be employed. This is probably the most critical stage of exploration since, depending on its results, decisions involving high costs and potential costs have to be made. If a decision is made that a potential ore body has been located, the costs of exploration will then dramatically escalate, often at the expense of other prospects. If it is decided to write a prospect off after this stage, there is always the possibility that an ore body has been missed. 1.5.3 Resource Evaluation Drilling This stage provides answers to economic questions relating to the grade, tonnes and mining/metallurgical characteristics of the potential ore body. A good understanding of the nature of the mineralization should already have been achieved – that understanding was probably a big factor in the confidence needed to move to this stage. Providing the data to answer the economic questions requires detailed pattern drilling and sampling. Because this can be such an expensive and time-consuming process, this drilling will often be carried out in two sub-stages with a minor decision point in between: an initial evaluation drilling and a later definition drilling stage. Evaluation and definition drilling provide the detail and confidence levels required to proceed to the final feasibility study. 1.5.4 Feasibility Study This, the final stage in the process, is a desk-top due-diligence study that assesses all factors – geological, mining, environmental, political, economic – relevant to the decision to mine. With very large projects, the costs involved in evaluation are
1.6 Maximizing Success in Exploration Programmes 7 such that a preliminary feasibility study is often carried out during the preceding resource evaluation stage.The preliminary feasibility study will identify whethe as well as ide 1.6 Maximizing Success in Exploration Programmes targ s.Of the small um The toat be initially generated in order to provide one new mine discovery will vary accord- ing to many factors (some of these are discussed below)but will generally be a large number.Some idea of what is involved in locating an ore body can be gained by considering a prospect wastage or exploration curve(Fig.1.1).This is a graph on which the number of prospects in any given exploration play (the vertical axis) is plotted against the exploration stage reached or against time,which is the same thing()The large spects initially generated declin through the exp ation sta s in an manne the prospec astage c 之 ve. On Fig.1.1 ed A repres successful exploration play,but in this case,although fewer prospects were initially generated,the slope of the line is much less than for play A.It can be deduced that the prospects generated for play C must have been generally of higher quality than the prospects of play A because a higher percentage of them survived the initial exploration stages.The line B is a more typical prospect wastage curve:that of a failed exploratic on play It should be from Fig.1.1 that there are only two ways to turn an unsu 器ee山ut or the explorationist has to get smarter (i.e.decrease the rate of prospect wastage and hence the slope of the exploration curve).There is of course a third way:to get luckier. Getting bigger does not necessarily mean hiring more explorationists and spend- ing money at a faster rate.Prospects are generated over time,so the injunction to get bigger can also read as"get bigger and/or hang in there longer.There is,howev usually a limit to the of w The limit prospec cts which can be gene ies that can be generated by the explorat are to be found in the confidence of the explorationist or of those who pay the bi This factor is often referred to as"project fatigue".Another common limiting factor is the availability of ground for exploration.In the industry,examples are legion of
1.6 Maximizing Success in Exploration Programmes 7 such that a preliminary feasibility study is often carried out during the preceding resource evaluation stage. The preliminary feasibility study will identify whether the costs involved in exploration are appropriate to the returns that can be expected, as well as identify the nature of the data that must be acquired in order to bring the project to the final feasibility stage. 1.6 Maximizing Success in Exploration Programmes Obviously not all prospects that are generated will make it through to a mine. Most will be discarded at the target generation or target drilling stages. Of the small numbers that survive to evaluation drilling, only a few will reach feasibility stage, and even they may fail at this last hurdle. The total number of prospects that have to be initially generated in order to provide one new mine discovery will vary according to many factors (some of these are discussed below) but will generally be a large number. Some idea of what is involved in locating an ore body can be gained by considering a prospect wastage or exploration curve (Fig. 1.1). This is a graph on which the number of prospects in any given exploration play (the vertical axis) is plotted against the exploration stage reached or against time, which is the same thing (the horizontal axis). The large number of prospects initially generated decline through the exploration stages in an exponential manner indicated by the prospect wastage curve. On Fig. 1.1, the curve labelled A represents a successful exploration play resulting in an ore body discovery. The curve labelled C represents another successful exploration play, but in this case, although fewer prospects were initially generated, the slope of the line is much less than for play A. It can be deduced that the prospects generated for play C must have been generally of higher quality than the prospects of play A because a higher percentage of them survived the initial exploration stages. The line B is a more typical prospect wastage curve: that of a failed exploration play. It should be clear from Fig. 1.1 that there are only two ways to turn an unsuccessful exploration programme into a successful one; the exploration programme either has to get bigger (i.e. increase the starting number of prospects generated) or the explorationist has to get smarter (i.e. decrease the rate of prospect wastage and hence the slope of the exploration curve). There is of course a third way: to get luckier. Getting bigger does not necessarily mean hiring more explorationists and spending money at a faster rate. Prospects are generated over time, so the injunction to get bigger can also read as “get bigger and/or hang in there longer”. There is, however, usually a limit to the number of worthwhile prospects which can be generated in any given exploration programme. The limits are not always (or even normally) in the ideas or anomalies that can be generated by the explorationist, but more often are to be found in the confidence of the explorationist or of those who pay the bills. This factor is often referred to as “project fatigue”. Another common limiting factor is the availability of ground for exploration. In the industry, examples are legion of
1 Prospecting and the Exploration Process THE EXPLORATION OR PROSPECT WASTAGE CURVE IDEAS PROSPECTS RESOURCES ORE B eaeon Time Exploration Stage Fig.1.1 These curves show how,for any given exploration programme.the number of prospects decreases in an exponential way through the vanous exploration stages.In a programme bas am (eurve Most programmes(curve B)will fall somewhere between these two curves exploration pro grammes,the earlie with an unsuccessful exploration programme or to cut one's losses and try some other province can be the most difficult decision an explorationist ever has to make Helping the explorationist to get smarter,at least as far as the geological field aspects of exploration are concerned,is the aim of this book.The smart explo- rationist will generate the best quality prospects and test them in the most efficient and cost-effective manner.At the same time,she will maintain a balance between as to maintain a ous fow of dir rected activity lead- .The achievem RedepcPonm ent of a good rollover rate of prospects is a sigr
8 1 Prospecting and the Exploration Process Time Exploration Stage Number of Prospects IDEAS PROSPECTS RESOURCES ORE Research; Conceptual studies Target generation Target drilling Resource evaluation Resource definition Feasibility Studies Mine THE EXPLORATION OR PROSPECT WASTAGE CURVE Fig. 1.1 These curves show how, for any given exploration programme, the number of prospects decreases in an exponential way through the various exploration stages. In a programme based largely on empirical methods of exploration (curve A), a large number of prospects are initially generated; most of these are quickly eliminated. In a largely conceptual exploration program (curve C), a smaller number of prospects are generated, but these will be of a generally higher quality. Most programmes (curve B) will fall somewhere between these two curves groups who explored an area and failed to find the ore body subsequently located there by someone else, because, in spite of good ideas and good exploration programmes, the earlier groups simply gave up too soon. Judging whether to persist with an unsuccessful exploration programme or to cut one’s losses and try some other province can be the most difficult decision an explorationist ever has to make. Helping the explorationist to get smarter, at least as far as the geological field aspects of exploration are concerned, is the aim of this book. The smart explorationist will generate the best quality prospects and test them in the most efficient and cost-effective manner. At the same time, she will maintain a balance between generation and testing so as to maintain a continuous flow of directed activity leading to ore discovery. The achievement of a good rollover rate of prospects is a sign of a healthy exploration programme
18 Exploration Feedbacks 9 1.7 Different Types of Exploration Strategy The exploration cur eprovides a way of on methods aspect of day expl on proces s.Some pread system mical me urements an typically result in the production of large numbers of anomalies.This is an empirical exploration style.Generally little will be known about any of these anomalies other than the fact of their existence,but any one anomaly could reflect an ore body and must be regarded as a prospect to be followed up with a preliminary assessment- usually a field visit.Relatively few anomalies will survive the initial assessment pro- cess.The exploration curve for a programme that makes use of empirical pro generation spect n will therefore have a very steep slope and look so mething like th e uppe ve(A)of Fig.1.1. The opposite type of prospect generation involves applying the theories of ore forming processes to the known geology and mineralization of a region,so as to predict where ore might be found.This is a conceptual exploration approach Conceptual exploration will generally lead to only a small number of prospects being defined.These are much more likely to be"quality"prospects,in the sense that the chances are higher that any one of these prospects will contain an ore body compared to prospects generated by empirical methods.An exploration play based on eptual ration will hay a relatively flat exploration and will nble the ower line(curve C)on Fig.1.1 Empirical conceptu and targeting are two end members of spectrum of exploration techniques,and few actual exploration programmes wou be characterized as purely one or the other Conceptual generation and targeting tends to play a major role where there are high levels of regional geological knowl edge and the style of mineralization sought is relatively well understood.Such conditions usually apply in established and well-known mining camps such as(for example)the Kambalda area in the Eastern Goldfields of Western Australia.the amp in the Canadian Abitibi Province or the Bushveld region of Sou Africa.Em cal techni tend to play a gre ole in progra he he leve egiona knowledge are much lower and oprogm employ elements of boto ical approaches and their exploration curves lie somewhere between the two end member curves shown on Fig.1.1. 1.8 Exploration Feedbacks There are many.many times more explorationists than there are orebodies to be found.It is entirely feasible for a competent explorationist to go through a career Greenfield exploration is where there are no pre-existing mines or prospects.This contrasts with brownfield exploration,which is conducted in the vicinity of existing mines
1.8 Exploration Feedbacks 9 1.7 Different Types of Exploration Strategy The exploration curve provides a convenient way of illustrating another aspect of the present day exploration process. Some regional exploration methods involve widespread systematic collection of geophysical or geochemical measurements and typically result in the production of large numbers of anomalies. This is an empirical exploration style. Generally little will be known about any of these anomalies other than the fact of their existence, but any one anomaly could reflect an ore body and must be regarded as a prospect to be followed up with a preliminary assessment – usually a field visit. Relatively few anomalies will survive the initial assessment process. The exploration curve for a programme that makes use of empirical prospect generation will therefore have a very steep slope and look something like the upper curve (A) of Fig. 1.1. The opposite type of prospect generation involves applying the theories of oreforming processes to the known geology and mineralization of a region, so as to predict where ore might be found. This is a conceptual exploration approach. Conceptual exploration will generally lead to only a small number of prospects being defined. These are much more likely to be “quality” prospects, in the sense that the chances are higher that any one of these prospects will contain an ore body compared to prospects generated by empirical methods. An exploration play based on conceptual target generation will have a relatively flat exploration curve and will tend to resemble the lower line (curve C) on Fig. 1.1. Empirical and conceptual generation and targeting are two end members of a spectrum of exploration techniques, and few actual exploration programmes would be characterized as purely one or the other. Conceptual generation and targeting tends to play a major role where there are high levels of regional geological knowledge and the style of mineralization sought is relatively well understood. Such conditions usually apply in established and well-known mining camps such as (for example) the Kambalda area in the Eastern Goldfields of Western Australia, the Noranda camp in the Canadian Abitibi Province or the Bushveld region of South Africa. Empirical techniques tend to play a greater role in greenfield8 exploration programmes, where the levels of regional geological knowledge are much lower and applicable mineralisation models less well defined. Most exploration programmes employ elements of both conceptual and empirical approaches and their exploration curves lie somewhere between the two end member curves shown on Fig. 1.1. 1.8 Exploration Feedbacks There are many, many times more explorationists than there are orebodies to be found. It is entirely feasible for a competent explorationist to go through a career 8Greenfield exploration is where there are no pre-existing mines or prospects. This contrasts with brownfield exploration, which is conducted in the vicinity of existing mines
10 1 Prospecting and the Exploration Process and never be able to claim sole credit for an economic mineral discovery.It is even possible,for no other reason than sheer bad luck,to never have been part of a team responsible for major new discovery.If the sole criterion for success in an explo- ration program is ore discovery,then the overwhelming majority of programs are essful,and most explorationists spend most of their time super ising failure But that is too ass es Ore disco is the ultim o.but not be the sole basi ate prize atic for me the quality of our effort The skill and knowledge of the experience xplorationis reduces thee of can never eliminate t.How dowe judge when an exploration program was well targeted and did everything right,but missed out through this unknown and uncontrollable factor?How do we know how close we came to success?If successful,what did we do right?And the corollary is this:if we are successful,how do we know it was not merely luck,rather than a just reward for our skills and cleverness?If we cannot answer these questions,it will not ossible to imr our game or repeat our succ What is ne ede ay to the of a n that is not depender ctualr discovery.Proba bly the of an exploration program is whe en able to c target from which at least one drill intersection of mineralisation with a potentially economic width and grade has been achieved.This"foot-in-ore"situation may of course have resulted from sheer serendipity rather than from any particular skill on the part of the explorer,but if an explorationist or exploration group can consistently generate prospects which achieve this result,then they must be doing something right.It will only be a matter of time before they find an orebody. 1.9 Breaking Occam's Razor Occam's razor is a well known philosophical principle that has universal applica- tion in all fields of problem solving.It states that.given a range of possible solutions the one that ests on few is alw ays to be preferred.For h rea son the maxim is n referred to s the ec omy,or even,with more impact,as the KISS principle (Keep It Simple.Stupid) However,Occam's razor-conjuring up an image of a ruthless slicing away of over complex and uncontrolled ideas-has a certain cachet which the other terms don't quite capture. All stages of mineral exploration involve making decisions based on inadequate data.To overcome this,assumptions have to be made and hypotheses constructed to guide decision making.Applying Occam's razor is an important guiding principle for this proce s,and every explo onist should apply y This is s fo and in all the pr and regional and semi-regional geological,geochemica Named after the fourteenth century English philosopher William of Occam
10 1 Prospecting and the Exploration Process and never be able to claim sole credit for an economic mineral discovery. It is even possible, for no other reason than sheer bad luck, to never have been part of a team responsible for major new discovery. If the sole criterion for success in an exploration program is ore discovery, then the overwhelming majority of programs are unsuccessful, and most explorationists spend most of their time supervising failure. But that is too gloomy an assessment. Ore discovery is the ultimate prize and economic justification for what we do, but cannot be the sole basis for measuring the quality of our efforts. The skill and knowledge of the experienced explorationist reduces the element of luck in a discovery, but can never eliminate it. How do we judge when an exploration program was well targeted and did everything right, but missed out through this unknown and uncontrollable factor? How do we know how close we came to success? If successful, what did we do right? And the corollary is this; if we are successful, how do we know it was not merely luck, rather than a just reward for our skills and cleverness? If we cannot answer these questions, it will not be possible to improve our game or repeat our successes. What is needed is a way to measure the success of an exploration program that is not dependent on actual ore discovery. Probably the best way to judge the success of an exploration program is whether it has been able to define a target from which at least one drill intersection of mineralisation with a potentially economic width and grade has been achieved. This “foot-in-ore” situation may of course have resulted from sheer serendipity rather than from any particular skill on the part of the explorer, but if an explorationist or exploration group can consistently generate prospects which achieve this result, then they must be doing something right. It will only be a matter of time before they find an orebody. 1.9 Breaking Occam’s Razor Occam’s razor9 is a well known philosophical principle that has universal application in all fields of problem solving. It states that, given a range of possible solutions, the simplest solution – the one that rests on fewest assumptions – is always to be preferred. For this reason the maxim is often referred to as the principle of economy, or even, with more impact, as the KISS principle (Keep It Simple, Stupid). However, Occam’s razor – conjuring up an image of a ruthless slicing away of over complex and uncontrolled ideas – has a certain cachet which the other terms don’t quite capture. All stages of mineral exploration involve making decisions based on inadequate data. To overcome this, assumptions have to be made and hypotheses constructed to guide decision making. Applying Occam’s razor is an important guiding principle for this process, and one that every explorationist should apply. This is especially true when selecting areas for exploration, and in all the processes which that entails, such as literature search and regional and semi-regional geological, geochemical 9Named after the fourteenth century English philosopher William of Occam