Post on 13-May-2023
Notes from Meetings with Jacques Dozy by Michael Thomsen Describing the Initial 1936
Discovery of the Ertsberg, Dom and Grasberg Outcropping Copper Deposits, Irian Jaya, Indonesia
by
Michael B. Thomsen Denver, Colorado
Abstract: In 1983 Jacques Dozy visited the mining operations of Freeport Indonesia Incorporated at Tembabapura. He was hosted by the Geology Department led by Michael Thomsen, Chief Geologist of Freeport Indonesia, and Delos Flint, Vice President and Chief Geologist of Freeport Minerals Company. Dozy’s visit encompassed a number of meetings and discussions with various individuals on site and included a helicopter tour of the area. This paper is an attempt to document that visit and the detailed discussions that were held with Jacques Dozy, the original discoverer of the Ertsberg district. Jacques passed away in 2004 in The Hague, Netherlands. Key Dates in the Exploration and Development of the Ertsberg Copper District:
1936 Colijn/Dozy expedition to the Carstensz region
1939 Dozy publication noting the discovery of the Ertsberg (Dutch for ‘Ore Mountain’)
1960 Freeport expedition by Delos Flint & Forbes Wilson, ‘re-discovery’ of the Ertsberg
1978 - 1988; Decade of Discovery and the Creation of the Ertsberg Copper District:
Ertsberg East (Gunung Bijih Timur ‘ore mountain east’ in Indonesian)
IOZ (Intermediate Ore Zone)
DOZ (Deep Ore Zone, with the acronym also as a gesture to “DOZY’)
Dom (‘Cathedral’ in Dutch as named by Dozy)
Grasberg (‘Grass Mountain’ in Dutch as named by Dozy)
Kuching Liar (skarn adjacent to Grasberg)
Figure 1. Senior Geologist, Soebagio Soparman (left), Jacques Dozy (center left photo, and right photo) and Freeport Indonesia Inc. Chief Geologist, Michael Thomsen (right) in the geology office in 1983. Detailed discussions were held regarding the original Colijn/Dozy expedition and the discovery of the Ertsberg, Dom and Grasberg deposits by him in 1936. During our extended talks, it was obvious Dozy’s recall of his expedition decades earlier was excellent. A helicopter tour of the district by the geologic team gave Dozy a perspective on the area he had not experienced since his initial discovery 47 years earlier. The Discussions Open pit mining operations at the Ertsberg were ongoing and the second orebody in the district (Ertsberg East or Gunung Biji Timur; GBT) had just gone into production when Jacques Dozy visited Tembagapura in March of 1983. His interest in the operation was all encompassing with a particular emphasis on the comparison of ore types between the two skarn deposits; the original Ertsberg magnetite-chalcopyrite skarn and the Ertsberg East grossularite garnet-bornite skarn. My interest, as we had prepared for his visit for quite some time, was to gain an intimate understanding of his early thoughts and observations during the 1936 Carstensz expedition. His memories of that trip were amazing and one could still hear the excitement in his voice and the glint in his eyes as he was recalling the events of 47 years earlier. I considered it a great honor and a real privilege to have been able to spend this time with Jacques. Subsequent mail correspondence between us confirmed that he had a real ongoing interest in the geologic work that was being conducted at the Ertsberg.
Figure 2. Emerging from the mist of clouds at 11,000 feet elevation, the outcropping Ertsberg magnetite-chalcopyrite skarn deposit in this early photo gives a sense of what Jacques Dozy observed looking back from the Carstenszweide from his ‘Alpine Camp’ at the base of the Grasberg intrusive complex. Jacques relayed many stories from his initial sighting of the Ertsberg after emerging from an arduous climb up the glacial cirque headwall below the deposit. He initially didn’t know what this jet black mass of rock represented that was situated near the white and gray limestone cliffs behind it. After breaking open samples of the black talus at the base of the outcrop, even this petroleum geologist could easily identify the copper sulfide mineral, chalcopyrite. He was quite surprised, then intrigued, then immediately started thinking if this might be something other than a geologic curiosity. But even during his early observations of the potential size of this deposit, he didn’t think that anything could be developed in this unbelievably remote location. He did believe that it was of considerable interest to collect samples for future study and possible publication.
From Dozy’s personal observations:
“As we reached the top of the headwall, we saw the Ertsberg on our right. It was a black wall rising up several tens of meters with patches of green coper minerals. I walked around the base of the outcrop and it was all copper ore. At the base of the Ertsberg there was an accumulation of angular blocks of ore which had fallen off the deposit. I broke off pieces with my rock hammer which revealed bright sulphides of iron and copper. The chalcopyrite was visible in every piece, not small blebs but massive sulphide. These pieces were very dense.”
Dozy’s location of his ‘Alpine Camp’ as noted on his map (Plate 7) was a fortuitous spot as this was located near the base of the highest grade portion of the Grasberg porphyry deposit. Dozy’s field notes from that area describe disseminated sulfides including pyrite and chalcopyrite in the Grasberg diorite, secondary biotite and surficial deposits of iron oxides along the eastern edge of the Grasberg. From Dozy’s published 1939 report from his 1936 expedition:
“The contact zone at the foot of the Grasberg is rich in ores. On the NW side of the Carstenszweide several ferruginous springs with limonite terraces occur. Samples from the area are rich in quartz with intergrown biotite flakes. The abundance of biotite in minute flakes or clusters leads me to suppose that these rocks have suffered some thermal effects. The samples also contain a large number of grains of sulphides including pyrite and chalcopyrite.”
Figure 19 from that report is an image of a thin section of ‘biotitized granodiorite porphyry’. While Dozy did not know it at the time, he actually identified secondary biotite from the potassic core of the Grasberg mineralized porphyry. While this author has read many of the technical and geologic reports published on the Ertsberg district discoveries since the 1970’s, he has never seen reference to Dozy’s descriptions identifying samples of this potassic core of the Grasberg deposit; and this was identified by Dozy in 1939 ! The ‘porphyry copper model’ was not formulated with secondary biotite as a core constituent of the potassic alteration zone until the late 1960’s. This is another example of Dozy’s incredibly detailed observations during his expedition and subsequent evaluation of samples collected and taken back to The Hague for further study and lab work. Considering the very high copper grades of the Ertsberg skarns, one could assume that the core mineralizing hydrothermal system and porphyry might also have higher than ‘normal grades’ for a porphyry system. Observation of secondary biotite in a quartz-biotite altered granodiorite containing pyrite and chalcopyrite with iron oxide terraces being deposited from springs on the eastern side of the Grasberg would also lead one to believe that the Grasberg was a porphyry copper system. The outcropping footprint of this ‘Grassy Mountain’ of 2,000 meters by 2,000 meters would also suggest a world class size. The subsequent exploration and discovery of the Grasberg porphyry copper system confirm Dozy’s early observations.
Figure 3. Photo of the outcropping Ertsberg magnetite-chalcopyrite skarn orebody shows it in its pristine form that was seen by the Colijn/Dozy 1936 and the Wilson/Flint 1960 expeditions. In our discussions, Jacques was interested in the people who had worked and directed the exploration in the district since Del Flint’s re-discovery of the Ertsberg. Most of those individuals, including myself, came out of Freeport Exploration Company’s ranks and were hand selected by Del Flint, who was Freeport Mineral Company’s Chief Geologist. I had worked closely with Del Flint and Frank Nelson, an early explorer of the district, in the Company’s Tucson exploration office and Frank regaled many stories from his extensive work in Indonesia that I discussed in detail with Jacques. In the mid-1970’s Frank directed the exploration effort on the ‘Flint Extension’ which eventually became the Ertsberg East deposit. The Flint Extension is an area of outcropping garnet skarns containing primarily bornite and chalcopyrite along a fault bounding the skarns with vertical limestone cliffs. Interestingly, those limestone cliffs
contained huge cascading stains of malachite, a copper carbonate, extending for quite a long vertical distance. During his initial evaluation of the Ertsberg magnetite-chalcopyrite skarn, Del Flint noted these malachite occurrences and field mapped the mineralized garnet skarns to the east of the Ertsberg. The second discovery in the Ertsberg was in its formative stages by this recognition of mineralization by Del Flint. There has been a steady progression of exploration geologists who, over the years, have worked on and discovered the orebodies of the Ertsberg District, including the following: Delos Flint, Frank Nelson, Tom Doe, Michael Thomsen, Dave Potter, Steve Van Nort and others It was an honor to have been chosen by Delos Flint and to be given the responsibility to lead the Ertsberg exploration effort in the late 1970’s to the early 1980’s. Delos passed away in November 2014 in Palo Alto, California. I am proud to have known him and considered him my mentor. RIP my friend. Que vaya con Dios. It is accurate to say that every geologist who lived in Tembagapura recognized the tremendous potential of, initially the high grade skarns, and then the porphyry copper system at Grasberg. As one (if not all) of the geologists previously said “I looked at the Grasberg every day and wondered how big it could be. But the correct progression of exploration in the Ertsberg District dictated that the high grade skarns be explored and developed first, after which the Grasberg porphyry was finally evaluated and drilled. Del Flint mentioned to me after Grasberg was drilled, that since all the skarn deposits had been evaluated, the next biggest target was the porphyry at Grasberg. Every major copper skarn system in the world is associated with a mineralized porphyry copper system. As the Ertsberg, Ertsberg East, IOZ and DOZ skarns comprise possibly the largest copper skarn system in the world, the next logical step in the exploration sequence was to pursue the mineralizing porphyry system with the Grasberg being the obvious focus of attention. After it was pointed out to him by the author in 1982 that the Grasberg could be a world class porphyry copper deposit based on the size of its footprint and the extent of its outcropping sulfide and secondary iron mineralization, George Mealey, President and Chief Operating Officer of Freeport-McMoRan Copper Company, Inc., once commented to the author, “Mike, we need to discover and drill only high grade copper deposits greater than 2%. Will the Grasberg have grades over 2% Cu?” My answer had to be ‘no’ as no porphyry system in the world had grades greater than that. Considering that the price of copper in the early 1980’s was in the $0.60 per pound range, George was probably correct in his directive not to explore the Grasberg before all of the high grade copper skarn deposits were drilled and developed. From his book: GRASBERG, George Mealey writes:
“Our geologists knew from the beginning that Ertsberg couldn’t be the only ore body in the area.”
He was correct on that point.
Perhaps the most concise and accurate statement on the discovery of the Grasberg was made in a 1991 article in MINING ENGINEERING magazine:
“A methodical follow-up of all the anomalies logged since the project’s inception in 1967 led to a 1987 decision to return to the Grasberg area north of the Ertsberg pit.”
The Grasberg was the last of the outcropping areas identified by Dozy as a mineralized body that remained undrilled. While it did not have the grade of the main Ertsberg skarns, it made up for grade by its sheer size. When talking about future programs in the district, Jacques asked what new targets were going to be evaluated. We discussed the completion of the Ertsberg East delineation drilling program and moved on to a couple deep intercepts high grade copper intercepts beneath the Ertsberg East deposit which were scheduled to be further evaluated (these eventually led to the discovery of the IOZ and DOZ deposits). Jacques went on to ask about the Grasberg. We got into the discussion of profitability and copper grades. He clearly understood that feeding the mill with the highest grades was the priority. He admitted that the Grasberg probably did not have grades as high as the skarns. He was correct in that point. The progression of exploration and mine development in the Ertsberg district represents the classic example of the old adage that exploration in the shadow of the headframe has the highest chance for success. The Ertsberg certainly proved that point. When he left site, I was sad to say goodbye to this most interesting, intelligent and very polite individual. Jacques made a strong impression on everyone he met. He was thoughtful in his answers to our many questions and was very patient with our young team of geologists. Jacques was an ‘explorationist’ in the truest sense of the word. He was a petroleum geologist yet he discovered one of the largest copper-gold districts in the world at a time when he only wanted to trek to an equatorial glacier and climb one of the highest peaks in one of the most remote parts of the world. Sometimes, serendipity reigns for an explorationist. By keeping his eyes open and having an ever inquisitive mindset, Jacques made an impact on geologic history in a way that he could not have imagined at the time. Jacques Dozy passed away in 2004 in The Hague, Netherlands. RIP my friend.
Figure 4: Plate from the J. J. Dozy report: GEOLOGICAL RESULTS OF THE CARSTENSZ EXPEDITION 1936 identifying the area of the Ertsberg skarn and the Grasberg porphyry deposits. Ertsberg, Grasberg and Dom are outlined in red ovals.
Figure 5: Plate from the J. J. Dozy report: GEOLOGICAL RESULTS OF THE CARSTENSZ EXPEDITION 1936 identifying the Ertsberg and Dom skarn deposits.
Figure 6: Photo of the ‘Dom’ massive magnetite-chalcopyrite skarn deposit as seen in outcrop. Note the white roofed building and helipad in the extreme lower left corner of the photo for scale. Streaks of green-blue malachite extend down the face of the Dom for tens of meters.
Figure 7: Geologic map of the Ertsberg district by the Freeport Geology Department in 1979. On our helicopter tour of the district, Jacques observed from the air that the hanging wall fault of the Ertsberg East deposit can be projected west-northwestward across the Carstenszweide swamp to define the southern boundary of the Grasberg intrusive. Dozy also wondered at the time how far vertically downward the Ertsberg skarn extended when he first viewed the outcrop of magnetite skarn. As it was subsequently drilled, the Ertsberg’s form was in the shape of a vertical ‘tooth’ with one third of the deposit outcropping above ground.
Figure 8: Recent oblique airphoto of the Ertsberg-Grasberg Copper District. The original Ertsberg open pit (now a lake) is in the lower left corner of the photo. The Ertsberg East (Gunung Bijih Timur or GBT) underground block cave mine is in the right central portion of the deposit. The IOZ and DOZ underground deposits are situated beneath the Ertsberg East mine. The Grasberg open pit is located in the upper left quadrant of the photo. The limestone ridges in the upper portion of the photo form the backbone and highest points on the island of New Guinea.
Salutation to the author by Jacques Dozy and Del Flint written within Forbes Wilson’s book: THE CONQUEST OF COPPER MOUNTAIN
Appendix 3: Images of Ertsberg and Ertsberg East ore specimens
(Above) Photo of Ertsberg massive magnetite chalcopyrite skarn ore (5 in L-R)
(Above) Photo of Ertsberg magnetite chalcopyrite skarn replacing thin bedded carbonates.
(Above) Photo of Ertsberg chalcopyrite crackle breccia cemented by chalcedony.
(Above) Photo of Ertsberg East massive bornite-covellite-clay breccia from the hanging wall breccia zone. This style of mineralization represents the highest grade ore in the Gunung Bijih Timur (Ertsberg East) deposit.
Appendix 4: Books on the Ertsberg and Grasberg Deposits: Conquest of Copper Mountain by Forbes Wilson, 1981 Grasberg, Mining the Richest and Most Remote Deposit of Copper and Gold in the World by George A. Mealey, 1996
Miscellaneous Photos
Delos Flint Michael Thomsen Frank Nelson/Forbes Wilson
Capt Ted Stains diving beneath the clouds in the Bell 204 Ted and I had many enjoyable (and some challenging) flights in both the Bell 204 and Bell 206A JetRanger aircraft during exploration in the district. Our Sunday morning ‘reconnaissance’ flights throughout this remote region were some of the most amazing flights in this author’s experience. We travelled far and wide and usually ‘away from where we were supposed to be’.
Local native tribe members in the area
Michael Thomsen was Chief Geologist for Freeport Indonesia from 1979 to 1983. He was also Chief Geologist of Freeport Sulphur Company from 1984 to 1987. While in Indonesia, he led the team that delineated the Ertsberg East deposit and discovered the IOZ and DOZ deep skarns. While in New Orleans, he led the team that discovered the Diqla biogenic stratiform sulphur deposit in the North Sinai of Egypt and initiated the program that led to the Main Pass 299 caprock sulphur discovery offshore Louisiana. Michael currently resides in Denver, Colorado with his wife and son.