John Riley and Alfred Kaye witnessed the largest known diamond by tonnage in the western hemisphere
For over a century, Dr John Riley and Dr Alfred Kaye have observed and written about the Diamond Resource Company’s Siouvi-4 discovery, a large-diameter diamond by tonnage in Mont De Sale, the giant limestone-rich sub-basin of the Montanha limestone.
Riley is an emeritus emeritus professor at CalTech; Kaye served as Diamond Resource Company’s chief geochemist; they have observed similar-sized diamonds in numerous deposits in South Africa, Canada, and Australia.
In 1986, Dr Riley’s research on hardness led to the publication of his book, Small Dots Can Hunt a Full Life, which highlighted the role of phytoliths, living forms of rock that record the hardness of mineral formations over millions of years. He noticed that quartz crystals in large rocks of Siouvi-4 – this was a new discovery to the geologists of the day – were not as pore-dense as those in larger rocks.
What Riley later found after several years of digging was that the “small dots” had been synthesised by a rare mineral called ilmenite over hundreds of millions of years from fluorine in the acidic water of Mont De Sale. Riley and Kaye located the source water just a mile or so away. From the resulting mineral identification, the two discovered the region was likely an exceptional, previously-unknown area of mantle and magma close to the Atacama Desert in the Andes.
Siouvi-4 was located in July 2016. The time period of the hydrothermal plume which contained ilmenite aligns with seismic data from seismic surveys of the entire Carlin trend, near the Guadalupe Mountains at Carlin in Nevada.
Riley and Kaye have also set up a geochemical sampler that is collecting data on minerals in the waters of Lake Isabella, 90km southeast of Lake Tahoe. This location is called Lai Telling, and Lake Isabella feeds Lake Isabella.
Riley and Kaye have not announced when Siouvi-4 was discovered but it is likely that they will do so. Dr Kaye says the answer may surprise him and the diamond industry, as much of Siouvi-4 is not fixed in stone.
Cove Lodge, in the remote Sui Mountain Range in Diamond Resource Company’s Mont De Sale deposit. Photograph: David Crane/Corbis via Getty Images