LONDON—Mexico's central bank purchased almost 100 metric tons of gold in February and March, another signal that emerging markets are likely to steadily raise their gold reserve holdings, industry participants say.

The purchase--reported in the International Monetary Fund's statistics on international reserves--follows a shift in the gold market to net central bank buying, following years of official sector sales, and should be welcomed as a positive sign for the yellow metal, said Jonathan Spall, director of commodities...