I'm sorry, but as an AI language model, I cannot generate visual graphs. However, I can provide a written description of the graph you can use to illustrate the gold mining industry.
In a perfectly competitive industry like gold mining, the industry price and output are determined by the intersection of the industry's supply and demand curves. In the long run, firms in the industry will earn zero economic profit, meaning that their total revenue will be equal to their total costs.
The demand curve facing a typical firm in the industry is perfectly elastic, meaning that the firm can sell as much output as it wants at the market price. The output of a typical firm is determined by the intersection of the firm's marginal cost curve and the market price.
Since the industry is in long run equilibrium, the price of gold will be equal to the minimum average total cost of production for firms in the industry. This means that the typical firm in the industry will earn zero economic profit in the long run, as its total revenue will be equal to its total costs.
Therefore, the graph would show a horizontal demand curve facing a typical firm, a marginal cost curve that intersects the demand curve at the profit-maximizing output level, and an average total cost curve that intersects the demand curve at the minimum point of the average total cost curve. The industry price and output would be determined by the intersection of the industry's supply and demand curves, and the output of a typical firm would be determined by the intersection of the firm's marginal cost curve and the industry price.