May 10 (Reuters) - Australian shares scaled a near 15-month high on Monday boosted by gains in gold and iron ore miners on the back of firmer metal prices, and as shares in the country's top two casino operators jumped on a proposed merger.

The S&P/ASX 200 index rose 0.9% to 7,147 points at 0045 GMT, their highest since Feb. 21, 2020.

Heavyweight miners were the top boosts to the benchmark, rising 2.55%, with iron-ore giant Fortescue Metals Group Ltd up 4.57%, followed by Ioneer Ltd, gaining 4.23%.

Gold miners climbed 2.08% as the prices of precious metal edged to three-month highs.

Pantoro Ltd rose 4.88%, while Catalyst Metals Ltd gained 4.83%.

Casino giants Star Entertainment and Crown Resorts both hit multi-month highs after the former proposed an all-stock buyout of its larger rival in a deal valued at A$9 billion.

Across the Tasman Sea, New Zealand's benchmark S&P/NZX 50 index fell 0.53% to 12,662.4 points.

Shares in a2 Milk sank as much as 16.3% to a three-and-a-half year low after the dairy producer cut its annual sales forecast for the third time.

In other markets, Japan's Nikkei was up 0.86% at 29609.65 points and the S&P 500 E-minis futures advanced 0.3%. ($1 = 1.2736 Australian dollars) (Reporting by Riya Sharma in Bengaluru; Editing by Krishna Chandra Eluri)