The stock market posted solid gains on Monday, beginning the new quarter with a fast start. Investors were pleased to get some upbeat economic news from China, raising hopes that the world's second-largest economic power might be able to extend the bull market a while longer. Several sectors enjoyed strong showings, but a few companies had to deal with downbeat news that sent their shares lower. MAG Silver (MAG 2.26%), comScore (SCOR 1.55%), and Tricida (TCDA) were among the worst performers. Here's why they did so poorly.

MAG Silver gets a bit tarnished

Shares of MAG Silver fell nearly 7% after the Canadian silver miner reported its fourth-quarter financial results. The development-stage mining company said that work at its Juanicipio mine in Mexico is proceeding apace, with an extensive network of underground tunnels and detailed engineering for mine infrastructure continuing to develop. MAG doesn't have any revenue yet, but it has done its best to keep costs contained, and it has enough of a cash reserve to sustain current exploration activity for quite a while. MAG Silver investors have waited a long time, and today's drop suggests that they might be starting to lose their patience despite some reasonably encouraging findings.

Bars of silver engraved with weight and purity markings.

Image source: Getty Images.

comScore deals with departures

Investors weren't happy with comScore today, as its stock plunged almost 30% following senior executive departures. Both CEO Bryan Wiener and President Sarah Hofsetter are resigning from their respective positions, according to the company, and comScore named board member Dale Fuller as interim CEO to fill Wiener's place. Many had been optimistic about comScore's prospects for further growth, yet profitability has been elusive for the information and analytics specialist. Several Wall Street analysts followed up on the news by downgrading the stock, and it's now unclear exactly how comScore plans to move forward.

Tricida gives back a bit

Finally, shares of Tricida dropped 8.5%. The decline appeared to reflect some profit-taking following a huge move upward last week for the biopharmaceutical company. Tricida shares had climbed by nearly half in a single day following news that a phase 3 trial of its TRC101 metabolic acidosis treatment established significant benefits for chronic kidney disease patients, including reduced incidence of a drop in kidney function. Even after today's decline, the stock is still up more than 50% so far this year, and if an anticipated new drug application for TRC101 comes as planned later in 2019, it could be the breakthrough that Tricida investors have waited to see.