My father, an accountant and eventually Financial Director of a specialist industrial lubricants company, and my mother, a housewife although qualified as a Home Economics teacher, were keen hill walkers and mountaineers. When we were youngsters, they regularly took me and my brother on weekend trips from our various homes in and around Stoke-on-Trent, then a steel, coal mining and pottery manufacturing centre, in the English Midlands. Besides taking a keen interest in local fauna and flora, the latter stimulated by my mother’s knowledge of the subject, I also collected mineral specimens on old mine waste (mullock) dumps, among which were colourful oxidised copper minerals from the long abandoned Ecton mine in the Peak District and Great Orme mine in North Wales. Little did I know at the time that these were both unusual copper deposits in a limestone hosted, lead-zinc province (of a style referred to as Mississippi Valley-type) and, furthermore, that both were initially exploited in the Bronze Age (~1700 BC; Williams and Le Carlier de Veslud, 2019; Fig. 1.1).

Although not widely taught in schools in the UK, Geology was an optional subject at Longton High School, a rough-and-tumble, boys only state grammar school, founded in 1760, where I received my secondary education. There, I was a member of Brindley House, named in honour of James Brindley (1716–1772), a millwright and then pioneering canal designer and builder, who lived much of his life in the nearby town of Leek (Corble, 2005). Another Brindley, George (1905–1983), a distinguished clay mineralogist from Pennsylvania State University in the USA, had also been an alumnus there some 40 years earlier (Newnham, 1986). Given my antipathy to Maths, Physics and Languages (especially Latin), Geology seemed like an attractive option. The Geology course was taught by Tom ‘Soapy’ Purcell, a stalwart and long time inaugural Secretary of the local North Staffordshire Group of the Geologists’ Association, which caters for the UK’s amateur geological fraternity. He was prone to ill health so classes were sometimes held at home in his bedroom, which involved a much anticipated 30 km round trip cycle ride and afternoon tea served by his delightful wife. The course was rather unstructured and often involved reading articles that he selected from the latest issue of Proceedings of the Geologists Association, but the personalised tuition and freedom to read more than just standard texts certainly kindled my initial interest in Geology.

I graduated from high school with good grades in the final A level Geology, Geography, Chemistry and Use of English exams, but without a clear idea of what to study at university until one of my father’s friends from his World War II years in Italy gave me a book describing Geology as a career. The promise of an outdoor life and plenty of travel appealed and a few months later I began a BSc degree course in Geology with subsidiary Chemistry at University College London (UCL), part of the University of London. The Head of School had wanted me to sit the admissions tests for Oxford and Cambridge Universities, but my father discouraged me because he considered them too elitist.

In hindsight, the course at UCL provided a solid introduction to the main geological disciplines and prepared me for starting out on a career as a geologist, although it did not include Economic Geology. Indeed, the only reference to mineral deposits was a passing mention of magmatic platinum mineralisation during a one hour lecture on the Bushveld Complex in South Africa. Field mapping exercises in the Yorkshire Dales of northern England followed by six weeks in the sub-alpine Jura Mountains of Switzerland were particularly valuable as well as enjoyable, but most of the student field trips run by the departmental Greenough Club were missed because of my involvement with cycling, both touring and racing: activities that were a main pastime throughout my teenage years (Fig. 1.2). As the end of the three year course approached, I had more or less decided against a career in Geology and successfully interviewed for a trainee copywriter position with McCann Erickson (now McCann), the global advertising agency. However, my First-Class Honours degree was better than most of the lecturers at UCL had predicted (and I had hoped for), leading to Sydney Hollingworth, the Professor of Geology at UCL (Fig. 1.3), offering me the chance to participate in a joint research project between UCL Geology Department and the Instituto de Investigaciones Geológicas (IIG; currently Servicio Nacional de Geología y Minería [SERNAGEOMIN]), the Chilean Geological Survey (Fig. 1.4). Funding was to be provided by the former UK Ministry of Overseas Development.

Prof. Hollingworth was a well known geologist and geomorphologist specialising in the Pleistocene, and his Chilean project was focused on tectonic uplift of the Andes (Hollingworth, 1964). My task was to study the linkage between the geomorphological development of the Copiapó mining district in the southernmost Atacama Desert and supergene oxidation and enrichment of the numerous, relatively small intrusion-related, copper-bearing veins and breccia pipes (Text Box 1.1). The results, based on three three-month field seasons and complementary laboratory studies at UCL, were to be presented as a PhD thesis.

Text Box 1.1 – Supergene Oxidation and Enrichment

Supergene processes take place within and immediately beneath the weathering environment and are a direct result of the descent of oxygenated groundwater, fed by rainfall, in the unsaturated or vadose zone above the groundwater table. Copper deposits undergo particularly profound supergene effects, which were reasonably well understood 100 years ago (e.g., Emmons, 1917) and then further elaborated by Kennecott research geologists in the late 1960s (Anderson, 1982; see also Sillitoe, 2005). In the supergene environment, hypogene sulphide minerals – originally formed from hot, ascendant hydrothermal fluids – undergo oxidation to non-sulphide species, the nature of which depends importantly on the pyrite content of the hypogene ore and the neutralisation or buffering capacity of the host rock. Where pyrite contents are low and the neutralisation capacity high (Fig. 1.5a), copper-bearing sulphides, most commonly chalcopyrite (CuFeS2), oxidise largely in situ to hydroxycarbonates (malachite: Cu2(CO3)(OH)2, azurite: Cu3(CO3)2(OH)2) and silicates (chrysocolla) or, under arid climatic conditions characterised by more saline groundwater, to hydroxychlorides (atacamite and its polymorphs). The oxyhydroxide, goethite [FeO(OH)], is the chief accompanying iron mineral. In contrast, in pyritic ore with low buffering capacity, the acidic solutions generated by pyrite oxidation – a bacterially mediated process – dissolve the copper in hypogene sulphides and transport it downwards, leaving behind mainly potassium iron hydroxysulphate (jarosite: (K,Na,H3O)Fe3(SO4)2(OH)6), hematite (Fe2O3) and goethite, collectively termed limonite.

On reaching the groundwater table, a redox front, the copper is reprecipitated – also likely bacterially mediated (Sillitoe et al., 1996a) – as sulphides of the chalcocite group by replacement of hypogene sulphides, with chalcopyrite and several other sulphide minerals being more susceptible than pyrite (Fig. 1.5b). The chalcocite replacement process can at least double the hypogene copper content, resulting in a supergene enrichment zone from tens to >200 m thick. In situations where later uplift and concomitant erosion result in placement of a pyrite-bearing chalcocite enrichment zone above the groundwater table, hematite-dominant limonite either alone (Fig. 1.6) or with copper hydroxysulphates (brochantite: Cu4(SO4)(OH)6; antlerite: Cu3(SO4)(OH)4) are the distinctive oxidation products, the amount of the iron and copper species depending on the accompanying remnant pyrite content (Figs. 1.5c, 1.7). The cumulative or multi-cyclic enrichment resulting from oxidation of first cycle chalcocite zones can attain even higher copper contents (Fig. 1.5c).

Under semi-arid climatic and suitable hydrological conditions, some of the coppercharged supergene solutions can migrate laterally for distances of several kilometres through permeable piedmont gravel sequences instead of continuing their descent to the groundwater table, resulting in formation of exotic copper deposits (Münchmeyer, 1996; Sillitoe, 2005). Neutralisation of these acidic solutions induces copper precipitation as chrysocolla, atacamite and copper wad in the interstices of the gravels and immediately underlying, fractured bedrock.

Irrespective of the pyrite content of the original hypogene mineralisation, supergene processes can be economically important. Where oxidation takes place largely in situ, copper in the resultant oxidised minerals (and that in exotic deposits) can be extracted by irrigation of ore piles with sulphuric acid (heap leaching), which is a much less expensive process than copper recovery from the sulphide ore by flotation and subsequent smelting and refining. Supergene chalcocite-enriched copper ore has the obvious advantage of being higher in grade than most hypogene and supergene-oxidised copper deposits (Fig. 1.5b,c), irrespective of whether it is treated by heap leaching catalysed by aerobic iron oxidising bacteria or by flotation.

The chance to work in the Andes mountains, a dream for most people in those days, was too much to resist so I declined my job offer and in early July 1965 was onboard a British United Airways VC10 for the 22 hour flight to Santiago, Chile. After a couple of days in Santiago, I headed north by bus to Copiapó (Fig. 1.8), with a stop en route for passengers to take lunch. The set menu started with an artichoke, which I had never seen before and ate in its entirety with a knife and fork, spiky petals and all, much to the astonishment of my fellow passengers. Clearly, I had much to learn about South America!

The head of the IIG office in Copiapó, where I was to be based, was Francisco (Pancho) Ortíz who, years later in 1981, would be responsible for siting drill hole number 6 that discovered the fabulously rich supergene chalcocite enrichment zone at the Escondida porphyry copper deposit in northern Chile (Sillitoe, 1995a, p. 10–13; Ortíz, 2021; Fig. 1.8). Pancho assigned Osvaldo Farías (Faruco), a fearless former pirquinero (informal miner), to me as a field assistant, with whom I spent many weeks living in miners’ shacks, learning the rudiments of spoken Spanish and working underground in operating and abandoned artisanal mines. These were often accessed by climbing down free-hanging, steel wire rope ladders, ropes tied to the front bumper of the Land Rover or, at best, winched down the shafts in ore buckets (Fig. 1.9): activities that would be precluded by today’s rigorous safety culture. These unorthodox means of underground access were necessary because a key aspect of my work was to chart the vertical supergene profiles beneath different geomorphological landforms.

Tragically, Prof. Hollingworth died just before my second field season and it fell to me to take his ashes on the British United Airways flight to Chile in order to fulfil his wish of having them scattered in one of his favourite places in the north of the country, with a dramatic Andean backdrop (Fig. 1.10). The spot, still marked by a small cross and commemorative plaque (Fig. 1.11), merits mention in several popular tourist guidebooks. Roye Rutland (Fig. 1.4) then became my PhD supervisor until he emigrated to Australia to take up a professorship at the University of Adelaide and, eventually, become Executive Director of the Bureau of Mineral Resources and its successor, the Australian Geological Survey Organisation (currently Geoscience Australia). Eugen Stumpfl then took charge of me until he soon departed for the University of Toronto. My fourth supervisor – surely a world record – was Alan Clark who also soon left for Canada, to Queen’s University in Kingston, Ontario, but fortunately remained closely involved with the Chilean fieldwork. Hopefully, I was not a contributory factor in their respective decisions to leave UCL! Eugen Stumpfl (1931–2004) and, particularly, Alan Clark encouraged me to focus on supergene mineralogy, advice that has stood me in good stead ever since because of the proficiency gained in quickly identifying minerals in hand samples with a hand lens and scratcher. The mineralogical work at UCL was based on polished section microscopy and X-ray diffraction (XRD) plus wet chemical analysis but also included use of one of the first Cameca MS64 microprobes, a temperamental instrument that once in a while produced credible results.

The PhD research enabled me to learn a bit about Andean geology and metallogeny as well as some basic geomorphological concepts, to become conversant with the complexities of supergene mineralogy and processes and – on Alan Clark’s insistence – to improve my writing ability. The thesis and a short derivative paper (Sillitoe et al., 1968) concluded that the Copiapó mining district underwent two main intervals of supergene enrichment, both characterised by steely chalcocite group minerals, beneath two distinct planation surfaces between the early Eocene and late Miocene. Supergene profiles were then truncated during development of the regionally extensive Atacama Pediplain, which was completed by 11.5 ± 0.5 Ma when it was concealed locally beneath a distantly sourced felsic ignimbrite (see Section 3.1).

Consequently, partially oxidised remnants of chalcocite-enriched ore are commonly exposed at the pediment surface. Subsequent degradation of the Atacama Pediplain and related incision of transverse canyons, the present day river channels, eliminated supergene profiles, but incipient enrichment, characterised by powdery, sooty chalcocite occurred in places in the vicinity of the current groundwater table. Intensification of aridity, pyrite deficiency in the truncated supergene profiles and rapidity of the pedimentation process were considered as possible reasons for the absence of significant enrichment beneath the Atacama Pediplain, with the last of these being held primarily responsible. However, with the benefit of hindsight, progressive aridification may well have been the prime reason for the decreased efficacy of the enrichment process since the late Miocene.

The combined field and laboratory work documented the supergene mineralogy of the oxidised ± enrichment zones of 43 deposits and prospects in the Copiapó district. Djurleite (Cu1.96S) was shown to be the principal supergene chalcocite group mineral in both the steely and sooty varieties of chalcocite, with the latter thought to convert to the former as a result of maturation. Covellite (CuS) is a subsidiary component of sooty chalcocite but also occurs, along with the blaubleibender (blue-remaining) variety (Cu1+xS), as an initial oxidation product of chalcocite group minerals (Sillitoe and Clark, 1969). Malachite, chrysocolla, cuprite and complex, pitch-like mineral mixtures (which pirquineros call almagrado or almagre, literally translated as ‘to make blood run’, probably because it has the colour of dried blood) are the chief oxidised copper minerals, with chrysocolla dominating near-surface ore. Atacamite and paratacamite are less abundant oxidised species, which become dominant farther north in Chile due to higher chloride contents in groundwater consequent upon progressive intensification of aridity during the Miocene.

Once thesis writing was complete, I began to think seriously about future employment and applied to the Institute of Geological Sciences, forerunner of the British Geological Survey. After an uncomfortable interview trying to explain the intricacies of supergene processes, I was offered a position but without any indication of a job description. By then, mineral deposits had become my passion so I was rather concerned that I might end up mapping sedimentary rocks!

In late August 1968, with my PhD thesis now submitted, I was in the Geology Department at UCL, putting the final touches to a supergene mineralogy paper (Sillitoe and Clark, 1969), when the secretary called to say that Carlos Ruiz Fuller (1916–1997), Director of the IIG in Chile, had unexpectedly arrived and, in the absence of anyone more senior and because I spoke a bit of Spanish, would I take him for lunch. Although I had only met Don Carlos, as he was widely known, on a couple of occasions, I readily agreed because my finances were by then severely depleted and a free lunch beckoned. It turned out that Don Carlos had been attending the 23rd International Geological Congress in Prague but had had to escape westwards by train when Czechoslovakia was invaded by the armed forces of the Soviet Union (Schneer, 1995). After sharing a bottle of wine, he asked if I would like to work for the IIG and undertake a field based study of porphyry copper deposits and prospects in Chile. Undaunted by having only visited two producing porphyry copper deposits, El Salvador and El Teniente (Fig. 1.8; Text Box 1.2), during my PhD research in Chile, I telexed my acceptance the next day and then had to advise the Institute of Geological Sciences that I was unable to take up the recently offered staff position. That El Salvador mine visit in 1966 was not a career enhancing occasion because during a welcome dinner with Chief Geologist Lew Gustafson (1933–2023) and his staff at the rather fancy company guest house, I shook a bottle of ketchup without realising the cap was unscrewed and befouled a white wall with most of its contents. So, in late 1968, it was back to Chile but this time to live there and take up permanent employment – for what would be the first and only time in my life.

Text Box 1.2 – Major Porphyry Copper Deposits

Porphyry copper deposits, including associated skarns developed in carbonate wall rocks, account for roughly 70 % of the world’s current copper resources and production, with an extraordinary 30 % coming from the central Andes of Chile and southern Peru. There are 15 super-giant porphyry copper deposits worldwide, defined as those containing ≥25 million tonnes (Mt) of copper metal in measured and indicated resources (Laznicka, 1999; this tonnage is a bit larger than current annual global consumption). Twelve of them are in the American Cordillera, with six – Collahuasi, Chuquicamata, Escondida, Los Pelambres, Río Blanco-Los Bronces and El Teniente – in northern and central Chile (Fig. 1.8). Río Blanco-Los Bronces is the world’s largest copper deposit, with >200 Mt of contained copper (Irarrazaval et al., 2010).

Discovery of these central Andean super-giants spanned hundreds of years. Collahuasi, El Teniente, Chuquicamata and Río Blanco-Los Bronces were sites of relatively small scale, near surface, high grade mining activity in the 19th century, with initial exploitation of Collahuasi and Chuquicamata dating back to Inca times. Large scale mining and copper production began in the 20th century, in 1906 at El Teniente, 1916 at Chuquicamata and 1963 at Los Bronces (Parsons, 1933; Irarrazaval et al., 2010). The hydrothermal alteration zones at Los Pelambres and Escondida had been known for many decades, but the porphyry copper deposits were only discovered in 1969 and 1981, respectively, and the porphyry deposit at the site of the former Collahuasi copper vein deposit in 1979 (Sillitoe, 1995a, and references therein). However, initial copper production from Escondida, Los Pelambres and Collahuasi only began in 1990, 1992 (1999 at large scale) and 1999, respectively, emphasising the lengthy time lag between the discovery of major deposits and eventual mining (Sillitoe, 1995a; Schodde, 2012).

Harry Neumann, a recently graduated geologist from the Universidad de Chile in Santiago, was assigned as my national counterpart. We traversed approximately 50 prospects, working progressively from north to south and using the IIG offices in Arica, Iquique, Antofagasta, Copiapó and Santiago as logistical bases (Fig. 1.8). More than 20 months were spent camping without any sort of communication with the outside world so we were also forced to learn some basic vehicle maintenance and cooking skills. Using 1:10,000 scale colour aerial photographs as a base, we mapped the geology and structure of selected prospects, several of which subsequently became deposits and eventually mines. Our main focus was intrusive rocks, particularly porphyry phases, and hydrothermal alteration and its relationship to copper mineralisation. We had to teach ourselves how to recognise and map hypogene alteration mineral assemblages, such as potassic (K feldspar-biotite) and sericitic (quartz-white mica), and distinguish them not only from original magmatic mineral associations but also from the widespread superimposed effects of supergene weathering, including kaolinisation of feldspars and chloritisation of biotite (Section 4.2). We used hydrothermal alteration papers by Creasey (1966) and Meyer and Hemley (1967) and descriptions of porphyry copper deposits in southwestern North America (Titley and Hicks, 1966) as our main guides. Most of the prospects we mapped had either never been drilled or the core from shallow holes had not been archived so we did not have the benefit of seeing rocks from beneath the supergene weathering environment and had to rely almost entirely on surface observations. Consequently, sulphide minerals were rarely, if ever, observed and the species likely to be present had to be inferred from the supergene mineralogy, including the component minerals of limonite (Text Box 1.1).

Francisco (Pancho) Camus and Nicolás Saric were at the IIG office in Iquique while we were using it as our operational base and, although never working together, they became firm friends. Many years later, however, these contacts were instrumental in numerous assignments at the major porphyry copper mines and prospects controlled by CODELCO – the Chilean state copper corporation for which Pancho was the exceptionally successful Corporate Exploration Manager from 1990–2005 – and several smaller copper deposits mined and explored by Compañía Minera Pudahuel.

While based at the Copiapó office, I was excited to be asked by Pancho Ortíz to accompany IIG geologist Aldo Moraga on a reconnaissance helicopter flight in search of undocumented alteration zones in inaccessible areas east of Copiapó. Returning down the Copiapó valley, there was a loud cracking noise, the helicopter pivoted through 90° and then stabilised as it veered sharply right and descended precipitously before touching down and skidding along a single track dirt road for at least 50 m. The pilot shouted ‘salten!’ (jump) because of the imminent fire risk but, although fuel was pouring from the ruptured tank of the piston engine Hiller, it did not ignite. The three of us were lying on the road in fits of nervous laughter when we became aware of a fellow standing over us with a startled look on his face. He was the driver of a truck loaded with hand-cobbed copper ore (Fig. 1.12) who had witnessed the incident; he agreed to take us back to town, arriving just in time for the pilot to buy us a stiff lunchtime drink. This was my first ever helicopter flight and I was unaware that in an emergency a trained pilot could make a controlled landing by means of autorotation, whereby the main rotor is driven by upward airflow without any power from the engine. Notwithstanding this hair-raising experience, I went on to use helicopters extensively for remote site access in many parts of the world, albeit always with an increasingly judicious eye on pilot experience, aircraft maintenance and weather conditions, eventually clocking >1,000 flying hours (Fig. 1.13).

Following the election of Salvador Allende as Chile’s Marxist Socialist president in late 1970, the country became increasingly politicised, funds for fieldwork eventually dried up and I could see little future in continuing at the IIG. While flicking through a copy of Nature, I noticed an advertisement for two Shell postdoctoral research fellowships in biological or physical sciences. Following long discussions with my friend and colleague, James Stewart, from the UK Ministry of Overseas Development, with whom I was staying in Santiago, I decided to apply although without having much hope of success. However, there was an apparent problem because the submission deadline had just passed although applications postmarked before the deadline were to be accepted because of a postal strike in the UK. After persuading a young lady at the Santiago general post office to backdate the postmark on my application letter by a couple of days, its receipt was eventually acknowledged and, more surprisingly, I was successful, thanks no doubt to the topical nature of the proposed research: plate tectonics and metallogeny. So, with my porphyry copper project in Chile regrettably unfinished, I returned in late 1971 to the University of London, this time to the Royal School of Mines at Imperial College where Professor Rex Davies (1922–2016) had agreed to host me. Therefore, Marxism had conspired to get me back to Chile and then to leave prematurely but, crucially, had enabled me to spend almost three years immersed in porphyry copper geology: a fact I enjoyed sharing as chair of the porphyry copper session at the 27th International Geological Congress in Moscow in 1984.

Before returning to London, my work at the IIG gave rise to an interesting opportunity that undoubtedly influenced the rest of my professional life. The United Nations and Empresa Nacional de Minería, the Chilean state mining agency, were conducting a joint porphyry copper exploration project. Project geologists were mainly Canadians, with expertise in volcanogenic massive sulphide (VMS) deposits (so named because they comprise predominantly sulphide minerals), but unfamiliar with porphyry copper geology. Therefore, the project manager, Don Robertson, asked me to help out and, after being granted leave without pay by my boss, Don Carlos, I was engaged in a consulting capacity to map the principal target, Los Pelambres (Fig. 1.8). In early 1970, after a 22 km mule ride, I settled into my tent (Fig. 1.14) and began the geological and alteration mapping alone in steep, rugged terrain with ~1,000 m of topographic relief (Fig. 1.15a,b). This led eventually to siting my first ever diamond drill hole, which miraculously turned out to be the discovery hole of what is now Antofagasta Minerals’ Los Pelambres orebody, one of the world’s largest porphyry copper deposits (Text Box 1.2). As a result, in early 1971, the United Nations asked me to undertake the first of what became many assignments with Plan NOA-1 Geológico Minero in northwestern Argentina. Included in the initial itinerary was the Bajo de la Alumbrera prospect (Fig. 1.8) under investigation by a quasi-state agency, Yacimientos Mineros de Agua de Dionisio (YMAD), where, using goethitic limonite as a guide (Fig. 1.5a; Text Box 1.1), I recognised that potassic alteration and, in particular, a centrally located quartz-magnetite-rich zone hosted the highest copper values. On a second visit in 1973, prospect geology and alteration zoning were mapped and the recommended drilling programme led to initial definition of the porphyry copper-gold orebody (Fig. 1.16a,b), which was eventually mined from 1998–2018. So, what better way to launch a consulting career than involvement with two major porphyry copper discoveries, thanks to a modicum of relevant field experience, being in the right place at the right time and blessed with more than a bit of beginner’s luck.

During my two year postdoctoral fellowship at the Royal School of Mines, it proved possible to combine laboratory work, preparation of manuscripts for publication (Sillitoe, 1973a,b,c, 1974; discussed below) and fieldwork in the central Andean tin belt of Bolivia (Section 4.5) with continuing consulting assignments in Chile and Argentina. Nonetheless, a career in academia was still firmly in the back of my mind. As a consequence, I applied for an Associate Professorship at the University of Toronto, then a vibrant centre for ore deposits teaching and research. My application made it to the final two person shortlist and an invitation for interview. At that point I got cold feet, realised that my destiny was field based consultancy (Text Box 1.3) and withdrew my application, leaving the other interviewee, who later I found out to be Ed Spooner, to get the job unopposed. That decision committed me to spending the next 50 years of my life travelling the world and observing and mapping fascinating rocks in outcrop, diamond drill core and reverse-circulation drill chips.

Text Box 1.3 – What Does a Geological Consultant Do?

Independent geological consultants provide technical advice and services to exploration and mining companies, but act exclusively in a recommendatory capacity without any management or corporate obligations or responsibilities. They are paid a pre-agreed fee, either as a lump sum per assignment or a daily rate, but receive no company benefits, such as health insurance or pension contributions. Consultants may work for one or two dedicated clients or offer their services more widely, although the latter is generally more common as a means of maximising the amount of available work. During the early and mid-20th century, there were only a handful of consultants, predominantly experienced, white male geologists who had retired from senior technical or managerial positions in North American mining companies. Therefore, as I began consulting in the early 1970s when in my twenties and without having worked for a mining company, I was surely viewed by many as a young upstart. These days, a few independent consultants, like myself, are generalists, albeit commonly focusing on specific mineral deposit types (e.g., porphyry copper, epithermal gold, VMS), but there is an increasing tendency for consultants to offer specialist services in disciplines such as structural geology, geochemistry, petrology, mineralogy, remote sensing and resource estimation. However, there is a fine line between consultants, who advise their clients, and contractors, who provide technical services. Consulting companies of various sizes also provide multidisciplinary advice and services to the exploration and mining sector, perhaps most importantly in providing the pre-feasibility and feasibility studies used to underpin capital raising for mine development, but staff are employees and their duties are dictated by management.

The work carried out by independent consultants can be field or laboratory/office based or a combination of the two, depending on the discipline involved, although consultants who spend the majority of their time on field assignments are a dying breed.

A field based consultant, like myself, would spend anything from one day to several months on an individual assignment, with the work usually comprising geological and alteration mapping, reconnaissance logging of diamond drill core (Fig. 1.17) and/or reverse-circulation drill chips and analysis of geological, geochemical and geophysical data already accumulated by the company concerned and any predecessor companies. In house training of company geologists, commonly involving local or overseas field trips, is a frequent additional activity (Fig. 1.18a,b). During my early consulting years, in the 1970s–1990s, I spent a lot of time mapping, which commonly entailed several weeks at a project site, either camping or living in a container or trailer. These days, typical assignments would be much shorter and focus on field appraisals of prospects or creation or validation of geological models to be used for planning drilling campaigns and/or resource estimation purposes. The latter would require construction of one or two representative geological and alteration sections of deposits based on reconnaissance re-logging of drill core or chips and corresponding surface traverses. In contrast, a geochemical consultant, for example, might design a soil sampling programme or use specialised software to model multi-element geochemical data collected for surface or drill core samples by company personnel.

Every consulting assignment inevitably concludes with a client report, which I have always preferred to finish in one day before leaving the project site but most others prepare subsequently back in the office. Many consultants specialise in specific metallogenic provinces, typically near their places of residence, whereas others are truly international and travel frequently. Given the high cost of airfares, international consultants often need to carry out assignments for several clients on a single overseas trip, implying much longer times away from home base. Interestingly, in his autobiography, Ira Joralemon (1884–1975), a well known and highly successful American consultant, opined that the advent of air travel would make international geological consultancy unviable because there would be insufficient geological work to compensate for the many days or even weeks of paid time needed previously to travel by train or boat to distant locations (Joralemon, 1976). Fortunately, his prediction has proved to be incorrect.

In summary, independent consultants have no job security and numerous bosses albeit for short periods of time and, if field oriented, can anticipate long periods away from home and a disrupted personal life. In essence, the amount of work that consultants are able to get and the remuneration they are able to command are a direct reflection of their reputations and perceived or demonstrated abilities to add value to projects. In my opinion, a love of geology and its challenges are a prerequisite for long term satisfaction and success as a consultant.

As progressively more porphyry copper deposits were being discovered in the central Andes, southwestern North America, British Columbia, Philippines and elsewhere, other countries around the world became interested in exploring magmatic arc terranes within their own territories. As a direct result of my contributions to discovery at Los Pelambres and Bajo de la Alumbrera, the United Nations invited me to act as a consultant to a country wide porphyry copper exploration programme in South Korea and to carry out an initial porphyry copper assessment of Afghanistan for the recently formed United Nations Revolving Fund for Natural Resources Exploration (UNFNRE), an entity designed to be financially self sufficient by receiving a 2 % production royalty on any mineral deposit discovery (Carman, 1979).

On several visits to South Korea from 1975–78, I worked with Sahng Yup Kim and his exploration geochemistry team from the Korean Research Institute of Geoscience and Mineral Resources (KIGAM) at a time when the country was only a decade into its industrialisation and still a gritty, impoverished place, quite unlike the rich, sophisticated nation of today. Our programme failed to discover a significant porphyry copper deposit, which, with the benefit of hindsight, was probably due to a combination of unfavourable metallogenic factors shared with Japan, including a chemically reduced continental crust and dominance of subaerial volcanism by ash flow calderas (Sillitoe, 2018).

In 1977, when Afghanistan’s then President Daoud Khan was angering the Soviet Union and its Afghan Communist backers by making tentative overtures to the West, two months were spent travelling more than 5,000 km throughout Afghanistan, a significant proportion on dirt tracks and camel trails, in two 4 x 4 vehicles (Fig. 1.19). My companions were two geologists from the Afghanistan Geological Survey, S.M. Ghazanfari and Sharif Ahmad Ahrary (Fig. 1.20) – neither of whom could drive, a professional driver and me doubling as second driver. The job was to inspect as many potentially interesting copper occurrences as possible, with the aim of making an initial assessment of porphyry copper potential and proposing an exploration programme.

At the time, the Geological Survey had many Soviet staff so several of the reports we needed were written in Russian and had to be viewed at the Survey headquarters in the capital, Kabul. There was insufficient time for this, so one evening, in exchange for a few bottles of beer care of the British embassy, the Survey librarian helped us to load the required reports into one of the jeeps. The reports were then consulted at leisure during long summer evenings in the field, with Ghazanfari, educated at Lumumba University in Moscow, translating from Russian to Pashto, and Sharif, who had attended the International Institute for Geo-Information Science and Earth Observation (ITC) in the Netherlands, then translating from Pashto to English, and me taking notes. Our nights were spent sleeping in the open, commonly with our sleeping bags laid out on narrow stone built platforms alongside village mosques where women were excluded. My companions had to carefully explain to village headmen that I was a God fearing Englishman and not one of the many Soviets present in the country, who seemed to be universally disliked. We were told of cases of Soviets being publicly flayed alive in local villages, a fate I was particularly keen to avoid. Every few days we would buy a goat, bled to death and skinned as we waited, for our dinners, which were often prepared by and shared with our village hosts, eating without cutlery and only our right hands as is customary. Local purchases had to be receipted to justify my cash advance, resulting at the end of the mission in a shoe box stuffed with scraps of paper listing items in one or other of the two local languages, Pashto and Dari. I can only imagine the reaction of the accountants back in New York.

The only copper prospect in Afghanistan with economic potential at the time was Aynak, ~30 km from Kabul, which during our field visit was being drilled by a Soviet-Afghan team. It was of little interest for our porphyry copper search because the dolostone hosted mineralisation of late Neoproterozoic age is of sediment hosted type (Text Box 3.1; Taylor et al., 2011). The deposit was acquired by a Chinese consortium in 2008 but development has languished because of contractual issues with successive Afghan governments exacerbated by terrorism. The copper occurrences we were visiting, many of them skarns or veins, were generally more remote and locating them often involved long walks in inhospitable terrain or, if more fortunate, rides on either horse or camel back. A constant threat was attack by the large cream coloured Kuchi dogs that live with and protect sheep and goats in the mountains. One dark night, walking back to a village ahead of my two companions, I was saved at the very last minute when an attacking dog thought better of confronting my raised geological hammer head on.

In some parts of the country, we came across Kuchi nomads who would invariably invite us into the cool interiors of their large black goat hair tents where we would sit with the male elders on exquisite carpets to be served tea by their young daughters whose smiling faces were a welcome change from the obligatory niqab or burqa that was ubiquitous in towns and villages throughout the country. Afghanistan is a stunningly beautiful country of great contrasts, from the majestic, snow covered peaks of the Hindu Kush in the northeast to the deep blue desert lakes at Band-e Amir in the centre and the barren sand desert between the Helmand River and the border with Pakistan to the southwest. The geology of this border region was familiar because of my recent visits to the Saindak porphyry copper deposit (Section 4.3). We even clambered up and into the giant 6th century statues of the Buddha at Bamyan that were destroyed by the Taliban in 2001. There were plans for a followup visit to the selected project area in western Afghanistan in 1978 but, only months before, President Daoud Khan was deposed and assassinated by the Communist People’s Democratic Party of Afghanistan; the Soviets invaded a year later and commercial contacts with the West were effectively severed – yet another Marxist influence on my geological career (Section 1.2). The considerable porphyry copper potential of western Afghanistan remains to be realised because since our reconnaissance nearly 50 years ago the country has been too unsafe for mineral exploration to be carried out.