Complex sentence: O'Leary is also an active stock investor and has also ventured into gold investing, where he holds a 5 percent weighting in his financial portfolio but does not gold stocks issued by gold mining companies due to poor management and rising costs.
Split into simpler sentences: O'Leary is also an active stock investor and has also ventured into gold investing, where 5 percent weighting of his financial portfolio is invested in gold. However, he does not invest in gold stocks issued by gold mining companies due to poor management and rising costs.