﻿The quest for a fabled treasure trove containing jewels, gold and original Incan artefacts – and believed to have been buried on a South Pacific island by 18th century Spanish pirates – could be about to reach its dramatic conclusion.

But the decision to allow a Dutch American textiles magnate to use heavy machinery to dig on Chile’s sparsely populated Juan Fernández Islands has sparked an outraged response from archaeologists and environmentalists.

“The motive is profit, not archaeological interest,” said Alejandra Vidal, the representative of the Chilean College of Archaeologists on the National Monuments Council. “Given the equipment that will be used, there’s a very real risk of artefacts being lost or damaged in the process.”

Bernard Keiser, who has been searching for the hoard for more than two decades, has been granted permission to excavate a 400 sq metre plot near Puerto Inglés on Robinson Crusoe Island, one of the three main volcanic islets that make up the Juan Fernández Archipelago 600 miles off the Chilean coast.

Chile’s National Forestry Corporation’s (Conaf) decision came even though the islands are protected by both national and international law, said Valentina Durán, the director of the Environmental Law Centre at the University of Chile’s law faculty.

“The area given over for the dig is doubly safeguarded, as it lies within the Juan Fernández national park and was also designated a Unesco biosphere reserve in 1977,” she said.

“Regulations are particularly stringent for foreigners to dig on sovereign Chilean soil in sites considered archaeological monuments ... What is clear from this case is that we need better protection, institutions and clearer laws for protected areas,” said Durán.

Adding to the controversy, Pablo Mira, the regional director of Conaf for Valparaíso – under whose jurisdiction the islands fall – was abruptly dismissed from his post in September. Mira had been a vocal opponent of the treasure hunt, but Chilean authorities have insisted that his dismissal was unrelated to the excavation permit.

Facebook Twitter Pinterest A 1758 map of Robinson Crusoe Island. Photograph: Antiqua Print Gallery/Alamy Stock Photo

Keiser, who could not be reached for comment, used scanning equipment to pinpoint a possible location after an exhaustive and expensive search that has thus far been conducted manually due to the area’s conservation status. He now reportedly believes that the treasure is hidden in a synthetic tunnel beneath a thick slab of rock.

José Manuel Rebolledo, the executive director of Conaf, has said that the necessary evaluations were made in order to guarantee that the dig will not affect the national park in any way.

If successful, Keiser’s search could put to rest the 300-year-old mystery surrounding the exact nature of the riches accrued by the Spanish sailor Juan Esteban Ubilla.

According to historical record, Ubilla accumulated the hoard – said to be worth $10bn – on his travels along South America’s Pacific coast in the early 18th century. He buried it in the remote Juan Fernández Islands when his ship was intercepted by the British navy admiral Lord Anson in 1714.

The haul is rumoured to contain original gold statues from Peru – including a necklace belonging to the wife of the last Inca emperor, Atahualpa – as well as 800 barrels of gold and silver coins.

Facebook Twitter Pinterest In 1704, the Scottish sailor Alexander Selkirk was marooned in the archipelago for four years. Photograph: Glasshouse Images/Alamy Stock Photo

A crew sent to recover the treasure in 1761 under the command of the British navigator Cornelius Webb found the hoard and loaded it aboard their ship. However, a mast split in bad weather as they were leaving the island and Webb was forced to turn back and rebury the hoard.

Webb then drew two treasure maps and wrote out coded instructions, one of which he sent back to England. Keiser acquired the second copy in 1998 from the family of the Chilean politician Luis Cousiño.

In 1704, the Scottish sailor Alexander Selkirk was marooned in the archipelago for four years, inspiring Daniel Defoe’s novel Robinson Crusoe – after which one of the islands was renamed in 1966 in a bid to increase tourism.