The copper futures contract has jumped to a two-year high in recent weeks, with the brown metal lifting above the 50-month exponential moving average (EMA) and entering its first bull market in more than four years. Improved China and emerging market growth has underpinned the long-overdue rally, along with continued speculation about U.S. infrastructure investment promised by the Trump administration.

The new uptrend should offer buying opportunities in copper-exposed equities, which have traded poorly in the first half of 2017. That shines a spotlight on the iPath Bloomberg Copper SubIndex Total Return ETN (JJC), the only pure copper fund play. Meanwhile, it is harder than it sounds to find traditional equity plays because most sector choices have diverse operations that include non-copper exposure. (See also: Commodities: Copper.)

The iPath Bloomberg Copper SubIndex Total Return ETN (JJC) holds $70.1 million in assets in 2.1 million outstanding shares that turn over just 74,000 shares per day. A relatively high expense ratio at 0.75% reflects the instrument's unique positioning because it is the only fund with direct copper exposure. Fortunately, bid/ask spreads are relatively tight, rarely expanding beyond five to eight cents. (For more, see: Want to Invest in Copper? Read This First.)

The fund came public at $50.40 in 2007 and topped out at $58.40 in the first quarter of 2008. It plunged with world markets during the economic collapse, hitting an all-time low at $17.97 in December 2008. The subsequent recovery unfolded at the same trajectory as the decline, completing a V-shaped pattern that reversed less than three points above the 2008 high in 2011.

JJC posted a higher low in early 2016 after descending for nearly five years and built a narrow basing pattern, followed by a November breakout that mounted the 50-week EMA for the first time since 2013. Resistance at $31.50 stalled progress through the first half of 2017 before giving way to a July breakout that has set off a fresh round of buying signals. Price structure now suggests that pullbacks between $31 and $32 should offer low-risk buying opportunities. (See also: Nearby Support Suggests Now Is the Time to Buy Base Metals.)

Southern Copper Corporation (SCCO) also mines small amounts of molybdenum, zinc, silver, lead and gold. The stock broke out of a multi-year basing pattern in 2001 and entered a long-term uptrend that topped out at $47.75 in 2007. Southern Copper shares fell into the single digits in 2008 and bounced less than three points above the prior high in 2010, ahead of a decline that found support in the lower $20s in 2013.

Multiple tests at that level into the second half of 2016 yielded a breakout that stalled within 11 points of resistance in February 2017. A rounded consolidation since that time has attracted heavy buying interest that could support a third quarter breakout into the contested zone. Given its bullish positioning, this market leader could offer the most profitable play on the copper uptrend. (For more, see: Top 5 Copper Stocks for 2017.)

Freeport-McMoRan Inc. (FCX) holds the world's top slot in copper production, but it is a watered down play due to the company's broad diversification. In addition to precious metals exposure, Freeport spent $9 billion to enter the energy market at the perfectly wrong time in 2012, and the stock paid the price with a decline to a 15-year low in January 2016. According to 2015 data, 67% of revenues come from copper, 11% from petroleum products, 10% from gold and 5% from molybdenum.

The steep decline tested the 2000 low at $3.38, reversing just 14 cents above that level and entering a recovery wave that stalled at resistance generated by the 2015 breakdown through support at $16.50. A pullback through the second quarter of 2017 built a base at $11 ahead of a bounce that is now gathering momentum. It looks like this impulse will test the 2016 high at $17.06, with a breakout favoring additional upside that could reach steep resistance near $20. (See also: Freeport-McMoRan Stock Breaks Out as Copper Soars.)

The Bottom Line

Copper continues to strengthen and has now broken out to a two-year high, entering a bull market that should underpin related equities. Southern Copper and the copper sub-index fund look like better bets than Freeport in this scenario due to Freeport's mixed metals and energy exposure. (For additional reading, check out: 3 Base Metal Charts to Watch.)

<Disclosure: The author held Freeport-McMoRan shares in a long-term account at the time of publication.>

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