Editor's Note: Mining Journal is making some of its most important coverage of the COVID-19 pandemic freely available to readers. For more coverage, please see our COVID-19 hub. To subscribe to Mining Journal, click here.

Mined copper production in the March quarter dropped 8% year-on-year and 4% quarter-on-quarter to 133,000 tonnes due to lower grades.

Rio now expects mined copper production in 2020 to be 475,000-520,000t, down from 530,000-570,000t, while refined copper guidance is now 165,000-205,000t from 205,000-235,000t.

Guidance was lowered due to a potential reduction in December half output at Escondida in Chile due to COVID-19 restrictions, and repairs at Kennecott Utah due to a 5.7 magnitude earthquake on March 18.

C1 cost guidance of US$1.20-1.35 per pound of copper was maintained.

Importantly, 2020 guidance of 324-334 million tonnes at C1 costs of $14-15 per tonne for the all-important iron ore division was maintained.

March quarter shipments were 72.9Mt, up 5% year-on-year, but down 16% quarter-on-quarter due to the impacts of Tropical Cyclone Damien.

The company said 16% of sales were priced by reference to the December quarter's average index lagged by one month, with the remainder sold at the current quarter or month average, or on the spot market.

About a third of March quarter sales were made free-on-board, with the remainder including freight.

Rio sold its one millionth tonne of ore from its portside trading trial in China.

Bauxite production was up 8% year-on-year to 13.8Mt due to the ramp-up of Amrun in Queensland.

Aluminium sales were flat at 783,000t.

"In these uncertain and unprecedented times we continue to deliver products to our customers with our first priority to protect the health and safety of all our employees and communities," Rio CEO J-S Jacques said.

"We are focused on maintaining a business as usual approach and have taken extensive measures to ensure we can do so safely.

"All of our assets continue to operate and we achieved a very robust production performance in the first quarter.

"Our world-class portfolio and strong balance sheet serve us well in all market conditions and are particularly valuable in the current volatile environment.

"Our resilience and value over volume strategy mean we can continue to invest in our business, and support our communities and host governments."

Rio noted Chinese demand continued to recover, but the outlook for the rest of the world remained more uncertain.

Iron ore and bauxite demand remained strong, copper demand was "reasonable" and aluminium demand contracted.

"To some extent, weaker commodity prices also reflect decreasing industry supply costs, which are falling due to a strong US dollar and tailwinds from lower energy and freight costs, partly offset by COVID-19 related expenditure," Rio said.

Rio said all of its major projects progressed in the March quarter, but were now being impacted by COVID-19 measures.

The company said its Pilbara iron ore replacement projects were on track and Koodaideri was still expected to start production early next year.

It warned the earlier stage Winu copper project in Western Australia could be impacted in the future by travel restrictions, though field activities were currently continuing.

The troubled Oyu Tolgoi expansion remains delayed by 16-30 months, but the schedule could be impacted further.

In Canada, construction of the Elysis aluminium centre in Quebec has been suspended, while the Falcon diamond study in Saskatchewan has been scaled back.

Capital expenditure for 2020 is now expected to be $5-6 billion, down from $7 billion, partly due to constraints, but also due to the favourable currency impact from the strong US dollar.

Capex planned for 2020 could flow into 2021 and 2022.

Morgans analyst Adrian Prendergast said the report did not change his positive view of Rio.

"A solid 1Q20 result with a strong performance from Rio's Pilbara iron ore operations," he said.

"Of chief interest for us are the continuing reports of high ongoing demand for high grade and high quality iron ore, while the COVID-19 impacts to 2020 copper guidance were disappointing."

Rio shares jumped 3.2% to A$91.37, the highest point since late February.