Nexa delivered solid and sustainable operating results in this cycle, overcoming the challenges imposed by Covid-19. We met our production guidance for 2020, of 313 thousand tonnes of zinc, despite having recorded a 13% decrease compared to 2019. The reduction is mainly due to the lower volume of ore processed in our Peruvian mines, which were affected by the temporary mandatory suspension imposed by the Peruvian government in response to the pandemic. We also produced 28 thousand tonnes of copper, 38 thousand tonnes of lead and 6,826 thousand ounces of silver.
The volume of metal sales also fell due to the drop in production at the Cajamarquilla and Juiz de Fora units, but was partially offset by the solid performance of Três Marias. The decrease reached 6% in the year-over-year comparison, to 585.4 thousand tonnes of metallic zinc and zinc oxide, but even so, we exceeded the guidance for the period.
Net revenue from our operations totaled approximately US$ 2 billion, accounting for a 16% reduction compared to 2019, impacted by lower average base metal prices and volumes traded on the world market.
Adjusted EBITDA in 2020 reached US$ 403 million, up 15% compared to the amount of US$ 349 million in 2019. This positive impact was driven by the decrease in costs and exploration and project evaluation expenses, and the depreciation of the Brazilian real against the U.S. dollar.
Mineral exploration and project evaluation costs decreased in 2020, mainly because Nexa revised its short-term capital allocation in response to Covid-19. The effects of the temporary suspension of such projects were reflected in the company’s cash flow estimates due to the impairment testes performed in 2020.
The Nexa Way program generated an estimated annualized positive impact on EBITDA of US$ 98 million in 2020, based on the initiatives implemented in 2019. We continue with the goal of reaching an improvement of at least US$ 120 million in annualized EBITDA by the end of 2021 through the program’s initiatives.
In 2020, investments in operations (Capex) totaled US$ 336 million, after deducting accrued tax credits of US$ 18 million with respect to our ongoing projects. Of this amount, 66% was allocated to expansion projects driven by the development of the Aripuanã project (US$ 187 million) and the deepening of the Vazante mine (US$ 13 million).
Liquidity and Indebtedness
As of December 31, 2020, our consolidated gross debt totaled US$ 2 billion, up 34.2% compared to the same period of the previous year (US$ 1.5 billion), mainly due to the appreciation of the Brazilian Real against the U.S dollar at the end of the fourth quarter and the partial drawn down of the BNDES loan agreement. At the end of the period, 77.7% (or US$ 1.6 billion) of gross debt was denominated in US dollars and 22.3% (or US$ 452 million) in Brazilian reais. The net debt to adjusted EBITDA ratio in the last twelve months was 2.29x, compared to 3.23x at the end of September, reflecting the improvement in results and cash generation.
We maintained strong liquidity. Cash and cash equivalents and financial investments amounted US$ 1.1 million at the end of the period. The total cash was sufficient to cover the payment of all obligations maturing over the next six years. The average maturity of the total debt was 5.4 years at an average interest rate of 4.68% per year.
In June, Nexa concluded an offering of US$ 500 million 6,500% senior unsecured notes, due in January 2028. The proceeds from this offering were used to repay certain existing financial debtedness, including the US$ 300 million revolving credit facility. The revolving credit facility remains committed until October 2024, and future disbursement under the credit facility will be subject to Nexa’s compliance with the relevant conditions, including applicable financial covenants.